350 or 400 Pontiac engine in '64 4X4?

[64_4X4_CustomCab]

I'm a newbie to the forum and I need some help with my 1964 Chevy C10 step side big back glass truck that is sitting on a 70's - 80's 4X4 frame. It doesn't have an engine nor a transmission. I have the opportunity to purchase a complete (carb to oil pan) Pontiac 350 out of a '68 Firebird, a Pontiac 400 short block and 2 Turbo 400 tranny's for a good price. I plan on using the truck just for fun and not planning on restoring it to original condition (more like a rat rod without the extreme modifications).

What's everyone's thoughts and things I need to think about in deciding if either of these engines are good solutions for the truck? How different are Pontiac and Chevy engines of the same cubic inch?

Thanks in advance for your input. I look forward to hearing everyone's thoughts.