'68 frame-off restoration - motor/fuel delivery system question

[Ms Bright]

I'm in the middle of a frame-off restoration on my '68 Chevy short bed. I am planning on going with a Ramjet 350 motor and need a new gas tank/fuel delivery system. I've done a bit of research and a fuel system comparable to the GenIV Vortec 5300s is what I'm leaning towards. I'm moving the gas tank to the back and have step-notched the frame to drop the bed to the ground (so my fat dog can load up w/o having to lift her 200lb butt). Where can I find existing fuel tank dimensions and/or specs, (in case I need to have the tank built custom using GenIV Vortec 5300s parts)? Also; has anyone found an automatic transmission compatible with the Ramjet motor? I've contacted GM for pricing and lead-time but, so far, no one has returned my calls.