compression
400, about.
350 heads will bolt to the 400 block. They will need to be drilled for the "steam ports" in the 400 block.
It will if the trans has Chevy bolt pattern.
using a 350 Chevy big block with a slightly modified 400 crank. best be a 4 bolt main too!
Absolutely. You will need special bearings for it, but it will bolt right in.
There is no need for a adapter plate, The 350 trans. bolt pattern is the same as a 400 trans bolt pattern. All Chevy transmission are interchangeable up to the year 2000
If it's a 350 from a Chevy, yes.
If the engine has main studs instead of bolts it should easily handle 400+.
yes
The main journals need to be turned down.
yes, but the main journals will need to be turned down to fit the 350 saddles
Yes a th 400 can be bolted to a 350 also a th350 and a power glide