From what I've seen, though they all seem to run tubular headers the port is pinched way down so they can get a typical 3/8" bolt with a 9/16" head on it to secure the flange.  Why Ford did this I have no idea.  Aftermarket headers have unpinched ports by just using regular 3/8" header bolts with a 3/8" head.  I don't know if Fox Mustang headers fit early chassis, but I have two good used sets if you want to try.  PM me if interested. 

MS wrote:

Foxbody factory headers do not fit 65-70 Mustang.  No way.

I have been using 289 Hipo reproduction iron manifolds. They don’t sound the same as headers, which you may say is good or bad, but they work quite well and do not cause problems.

Only difficulty I have encountered is on Edelbrock aluminum heads where a little aluminum has to be ground off so the manifold body clears where the deck on the head is thicker than stock. 

There are aftermarket “stock” manifolds being produced now that may or may not be an improvement.

Thanks for the heads up on that.
I am very uncertain about headers and definitely would never go with long tube headers (which they say perform the best), so I think manifolds are probably what I will stay with, unless someone can convince me otherwise.
Reading up on dyno test comparisons between the hipo manifolds and stock manifolds, there is basically no difference with performance. Surprising to me...

Where is all the love for try-y headers.

I looked at the cast iron GT ones but decided on the lighter try-y headers.
The stock tri-y’s that I have needed to be modified to accommodate the wider AOD,
The ceramic coating had to be removed at the welded joints. The welded areas were painted with silver bbq paint.

Rudi didn't say that the Tri-Ys were available in cast iron. He said he looked at the cast iron manifold that MS mentioned, but decided on the lighter Tri- Y header.

Maybe it's 'the-power-of-suggestion'.....I don't know butt......the slight tic-tic-tic of long tube headers at idle and low speed sure make me smile !!          (Heck....it could be leaky flange gaskets I don't know)
Floor shifters don't make a car any faster but........sure looks cooler'n column shifters.
Same with 4 tube long headers.....  just part of "the package" IMHO.
6sal6

It appears to be the driver side but you’ll need the right as well.

Greg B wrote:

I found this on Facebook marketplace. Says ford manifolds $25 each. Correct me if I am wrong, but the bottom left sure looks a lot like a hipo manifold.

These are located in Illinois, about 75 miles Northwest of Terry.

That one looks to me like a 351w manifold.  Don't know about the rest although I recognize some of them.
 

Toploader wrote:

I was wondering about hipo manifolds, but after dyno test comparisons shown in the article I read, they claim there is no benefit to them when compared to stock manifolds. Surprised me...

My guess is that the HiPo manifolds made more power on the HiPo, otherwise Ford wouldn't have bothered to create them in the first place.  However, all the power may well be gained in the upper RPM range where a regular hydraulic cam 289 or 302 isn't going to be able to go. 
 

Toploader wrote:

TKOPerformance wrote:

Toploader wrote:

I was wondering about hipo manifolds, but after dyno test comparisons shown in the article I read, they claim there is no benefit to them when compared to stock manifolds. Surprised me...

My guess is that the HiPo manifolds made more power on the HiPo, otherwise Ford wouldn't have bothered to create them in the first place.  However, all the power may well be gained in the upper RPM range where a regular hydraulic cam 289 or 302 isn't going to be able to go. 
 

I'm just not sure... Did you see the article where they did dyno runs and documented the torque and power outputs at set rpms and then compared between the stock manifold and the hipo manifold? There was basically no difference from what I read. Well... Maybe .02 or something.
So yeah, I don't know...

The article I remember seeing was in Mustang and Fords and only ran the engine to 4,800RPM (redline for a non HiPo 289).  At that RPM I wouldn't expect anything from HiPo manifolds.  HiPos were designed to run north of 6,000RPM.  I'll bet an A code 289 makes more torque at 3,000RPM than a HiPo too.  The two engines have the same displacement, but beyond that are really quite different animals.  In the end the question on any engine part being "good", "better", etc. has to do with the intended use and the combination.  If you have or plan a cam, heads, etc. then I would bet the HiPo manifolds are better than the standard ones, though probably not quite as good as headers.  If its a stock cam engine then its probably not worth anything other than bragging rights.