The pb-2 mounting plate is designed for 65-66, and aligns with the top two pedal support holes (as close as possible, still uses same holes)  I have only done a few hydroboost installs, and it was a long time ago, using a 98 Mustang hydroboost.

The pedal pin can be used to change pedal ratio, but you are limited by the geometry of the hydroboost unit as to where you can relocate it.

My comment as to using a 67 PB pedal and relocating the pivot upward 3” was based on your pictures where you obviously did not mount the pedal pin in a different location.  At least that was my perception when I looked at the pictures.  It appeared you still have the stock pedal pin location, which is NOT going to work right.

MS I should have provided more pictures and an explanation.  I  think the pin relocation from the kit would put things very close but I would still need to lower the HB unit itself.  The plate in the kit will interfere with the HB unit or I should say the hole in the PB-2 plate will as that hole location is to high.  If that hole was offset then it would work with the HB I am using.  Again I would still have to lower itto keep the push rod straight with the HB unit itself.

I was just hoping for a straight forward install and that is not what it will be.  lol

I plan on drawing everything out to get my angles and distance right.  I will also try to confirm the 3.75 to 1 ratio as I'm finding some say it may be 4 to 1. I think it will be a pretty straight forward install once I get everything figured out.  just need to relocate a couple of mounting holes and the stud location on the brake pedal.  

Vkt-66, I'm using an 03/04 cobra hydroboost so my install may vary slightly from yours.  As far as how it will need to mount to the brake pedal/firewall.

Stock 65-66 ratio is 6:1
The MustangSteve pb-2 conversion takes it to 4.1:1
The 67-69 pb pedal is 3:1
The 70 pb pedal is 3.5:1
2015-2020 pedal is 3:1

Just for reference...

So far it looks like the cobra brake pedal ratio is 4.63 to 1 and not 3.75 like I had thought.  The 4.63 is more believable and falls into the range of most of the other ratios on others.  Since I already bought the PB-2 kit I will just use the stud from the kit and set the plate aside for who knows what. 

Hoping I can get some work done this weekend.  It's almost impossible to work on the mustang with busy season at the hospital.  Another 12 hour day today but the pay checks are good.

Just curious because I don’t remember.  My 98 GT had a master cylinder with diagonal mounting flange. Is the cobra master cylinder the same?  Will you be using the cobra master cylinder?

Made some good progress today on the mounting of the hydro boost to my stock pedal.

All that time making drawings and trying to figure things out and all I ended up doing was Drilling a mounting hole 5/8 lower than the top bolt of the brake pedal bracket. The more I looked at things the more it looked like a straight forward mounting other than having the wrong ratio. This was with the top bolts from the hydro boost bracket fitting inside of the top bolt holes on the brake pedal bracket.

Once I lowered the mounting location by 5/8 I then clamped the pedals in the fixed location and it all lined up with my layout marks. I ended up lowering the stud down 5/8’s and and inward a 1/2 but this 1/2 was just a measurement. I actually fit the stud by scrubbing a circle from the ID of the pushrod. Then I took a die grinder to set the stud location. Then shoulder on the stud needs to be removed so I can fit the plastic washer and brake light switch. If I don’t remove the shoulder the MC rod will have an angle to it.

I also made a steel plate to mount to the inside of the firewall. This will provide a sandwich of the firewall between the HB plate and the plate I made. I will weld the plate to my brake pedal bracket.

I was hoping I could post pics from my phone, no luck.  My desk PC died today so I need to swap it out with my spare.

Good job RTM.

BB1

Making a little progress today.  I was able to get the holes drilled in the firewall and mock up the HB unit.  There's a side block that I think is there to relocate the lines for a better fit on the mustang/cobra.  I'm hoping I can remove this side block and just attach the lines to the side.  if not I think I can just as easily install 90 degree fittings to clear the hood hinge.  Other than that, I think the fit is pretty good and feels really solid.  

I'm thinking of maybe even running lines out through the inner fender and back to the PS pump from a lower approach to give the lines a hidden appearance.  

No luck with removing the block.  I either need 90 degree fittings or see if I can drill and tap access from the side of the block.

MS wrote:

Just curious. Do you have a wedge between the firewall and hydroboost so the top of the master cylinder fits level? If not, it might be contributing to your pedal ratio issue.
I am using a 2019 booster on my 56 F100, and it required a wedge 3/4” thick at bottom and 1/8” thick at the top.

Yes it still has the factory plate mounted to the HB unit itself that places the angle to keep the MC level.   Without the wedge I would end up with more clearance but the MC would not be level.  I'm guessing you meant clearance issues and not ratio issues.  The ratio is set up for 4.6 to 1, so that should be good to go.

I added an extra plate to the inside of the firewall for added support.  Just not sure if I will weld it to the pedal assembly or.

I believe the low pressure port is SAE 5/16-24 and I can purchase a banjo style fitting which will give me all the clearance I need.  I can buy the banjo fitting in either both ends, 6AN or have it attached to the line itself when the line is made.  

MS wrote:

From your picture, the unit needs to be angled upward. It points down, or is level, when it should angle upward.  The TOP of the plastic tank should be level, not the master cylinder centerline. This added wedge may also increase room for the fittings.

Are you sure about the pedal ratio?  Most modern mustangs were closer to 3:1. The wedge would improve the ratio.

Definitely weld your brace to the pedal support. You want the pedal support and the hydro unit to act as one piece, which removes any firewall deflection from the equation.

 
The unit is anglers up.  I researched the pedal ratio and only found one person who claimed they installed the same HB and the ratio was 4.63-1.  I had nothing else to go by.  I read a post that claimed a different ratio but had no way of confirming it.   I’m pretty sure I posted here that I was trying to figure out the 03/04 ratio.    If I need to change it then now would be the time.   Couple pictures showing the factory angled plate.   I did not mount the booster to the plate I made.   I added the plate to the inside of the firewall to help stiffen it all up plus mount the pedal support to it.  The factory angled plate is on the outside of the firewall.

You can install a longer pedal and mount the pedal pivot higher up if you need a lesser ratio.  Like the 67 power brake cars and all Mustangs after 1978.

Thanks for the pics showing the angle of the plate.  I am guessing the pic I saw of yours with the master cylinder pointing down must have been prior to tightening the studs. 

One other challenge I ran into was the brake pedal hitting the input body of the hydro unit before it was 100% activated.  It has been many years so I do not remember all the details like yesterday.  And I am not even sure about yesterday!