In one weekend by a backyard mechanic or small shop ... NO.
With a lot of time/money and chopping the engine bay down to nothing ... YES.
Yes
A V8 engine
YES, That is a direct swop.
Any smallblock Chevy engine will physically "fit" into a 85 Impala
Yes it will, It should already have a small block Chevy in it , if it's a V8.
Yes, but Chevy did not make a 400 in 1985. If the car already has a v8, it is already a Chevy engine. If it is a v6, it is still a Chevy engine, but you would need v8 wiring, brackets, exhaust,etc to make it work.
not eactly you will need a transfer case
Google "Jegs"
It will not work, but it will likely bolt in. The 4.3 is a very close relative of the small block V8
The only one I can think of is the exhaust Y-pipe may not fit from the 305 to the 350.
sure
NO it will not.