MustangSteve wrote:

I have been considering that very thing as part of the new tank installation.  On my F-100, I built an angle iron frame that fit around the tank flange, then the flange was sandwiched between that frame and the bottom side of the mounting frame, so the tank was bolted in from the bottom, with nuts welded to the top of the frame so you only had to use bolts from below.
The other thing I am considering doing, which appears would be very easy to do, is move the tank to the passenger side about 1/2" to allow clearance for exhaust and shackle R&R access on the driver side.  I am very surprised I have never thought of that before, or that no one else has mentioned doing it.  Since the passenger side tank drop-off area is tapered, it would be simple to cut the corners, lessen the taper, making that side more vertical, then make some sheetmetal corner fillers and weld them in.  Add a piece of steel to take up the driver side resulting gap.  Hose should be able to angle enough to move the tank 1/2".  Heck, even 1/4" of movement would be a big help when running 2-1/2" tailpipes.

A lot of work to gain 1/2" butt-lick you said....well worth it to help that cramped up side of the exhaust system!
6sal6
 

Mounting it underneath with a plate over top certainly wouldn't hurt, but remember, the main offender on these cars in a rear collision is the rubber fill neck hose rupturing allowing fuel to slosh/escape into the trunk area.  As mentioned above, the addition of a sheetmetal plate between the rear seat and trunk would be a large addition to the safety factor.  Also, even with the fuel isolated from the passenger compartment, if the car is rearended with enough force to rupture the tank there will also be whiplash issues unless highback seats with headrests are installed in the early cars.  While your at it, 3-point belts are nice to.

I've been wanting to do that for a long time too. There's a company that makes a shield, that is crazy heavy and very pricey, called tank armor. I have been trying to find a piece of SS sheet that doesn't break the bank, that my friend can Fab up for me. Not sure what thickness to go with, but was thinking 3/16". As far a seat divider, was thinking maybe aluminum sheet for that. Any thoughts?

I had considered a flat plate over the top of the gas tank, but in reality, if rearended, it is just going to get crumpled just like the tank will and gaps will be created between the plate and trunk floor.
Tht is why I have just left mine alone.  Nothing except a fuel cell will do the job completely. 

I think I posted this before, but I took the panels off of a dryer and cut them to fit behind the back seat. I sealed them with silicone caulk when I installed them. Figured it might keep some of the gas out of the cabin if ever get rear ended.

67 coupe.