If you are just going to cruise the car/highway I would just keep and freshen the 318 poly engine. They are a better engine than a 413. As mentioned before if it was a running car sure, parked since 1985, no.
Your opening 3 cans of worms. Big block where a small block was. 1)Trans is different bellhousing and ball and trunion front driveshaft joint, pushbutton campared to cable column/floor shift. 2) You probably will need 1965 C body, big block mounts. A 1964 Imperial is not a 1965 up C body. 3) all the accessory brackets do not swap, so you end up with accessories that have been dormant since 1985, water pump, fuel pump, power steering pump, (alternator excluded) so you can change them now or breakdown and change them later.
Yes this swap can be done. Chevy easy, no.