if you don't already have the 9", let someone else spend the big bucks and find something cheaper like an s-10 rear. s-10 owners routinely upgrade to 8-cyl engines without changing the rear. further, the s-10 rear is the correct width and bolt pattern.
for the tranny, i'd stick with the th350. it's lighter, takes less hp to spin, and it's plenty strong enough for a 350 hp small block.
don't overdesign your drivetrain. think efficiency.
ed
