Under bed fuel tank

[koda360]

I'm wanting to relocate the fuel tank under the bed, behind the differential. I have a 60 c-10, all the aftermarket "drop in" kits, show 64-66.
Other than the front end being torsion bars on the earlier models, what's the difference on the rear most portion of the frame? Is there a reason no one makes a kit for the 60-63?
I have measured my frame and compared it to the dimensions of the kits' tanks, everything seems like it would fit.... Maybe some fab work for brackets, straps, ect, which is fine. I just hate to drop that kind of money for a kit, only to find out it just wont work.

Any insight would be helpful, thanks in advance...