Hey Jeff,
I have a 1950 F1 & I used the 1970 Mustang tank because
it carries a bit more capacity - 22 gallons. It's pretty deep - If you mount it under the frame it will stick down a lot. I don't think you want your gas tank to be the lowest part of the truck back there when you bottom out.
It's a good project - If you are looking for a twist on how it's installed - figure out how to easily get the gas into the tank from the side of the bed/fender. It can be a chore to fill the tank up through the bed
if you have load in there.

Ben in Austin