It depends on whether or not the intake ports match on the cylinder heads. You can get that info from one of parts exchange guides you may find online.
typically 350 parts are more common and cheaper than the 400 parts.
Yes, if they were built with the standard Chevy bolt pattern.
no
No. The 400 is externally balanced, the 350 is internally balanced.
305 heads of course, 350 heads will fit for sure and possibly 400. obviously no big block heads will fit. a 305 with 400 heads gets you a little over 352. 350 with 400 heads is a 383. add and divide
no
Yes it will.
About 400 lbs.
Cast iron for a 307 or 350 unless they have 1.72" intake valves then its a 400 head
350
350, 400, 454
If it's a 350 from a Chevy, yes.