with due respect you are planning to revive a dead beast with severe cosmetic damage
for a 4000 cc 6 cylinder 90 HP 3 speed auto-transmission American car you will be needing more or less a Japanese equivalent engine, matching gear box to mate with differential. Toyota 4.0L Inline 6 Type 3FE engine or Type 5VZ 3.4L V6 from Land Cruiser will be right choice complete with Sensors, ECU and wiring.
however - in nutshell whatever you plan to invest it will be waste of money as in Pakistan Caprice is sold by weight for scrap due to scarcity of cosmetic & essential body parts