Yes they will interchange; everything behind the front header panel will interchange on those two cars.
The tail lights are interchangeable, the only difference is the chrome trim that was standard on the Caprice
No. Two very different generations and body styles.
Yes
yes
Can a 84 Chevy caprice classic fit on a 83 Chevy caprice classic
yes
Not likely as they're 2 totally different bodystyles
Kindly tell, what is P.C.D of stock Rim of chevrolet caprice classic 1981
Yes. 91-96 impala, roadmaster, caprice, and fleetwood rear end are all the same and will fit with no modifications.
No.... You need to change the whole back tail piece
No