You will have better luck over in the Rodder's section.
I'll bump this for a mod.
BTW, to answer your question, a small block isn't hard. Put A body manifolds on, push it over to the passenger side an inch or so, and it clears.
You can get small blocks over 400 cubes easily now.
A big block is going to be much tougher, mainly due to the steering. I realise you wnat to use what you have on hand, but it's a lot more work and will need more parts.