I have an old V8 engine that runs that I am taking out of an old boat. Could I just do a straight up switch with the current engine in my pickup?

 

No that marine engine heads are different then non marine with that said you can put a v8 in your truck just not a marine v8

 

I currently have a 350 sbc in my 85 pickup.
Your going to have to do a few things to get it to work, and work properly
Heres the list:
Custom motor mounts (or buy a pre made set off the internet)
If you want to run headers, they will need to be custom due to clearance issues
Lift kit to get the oil pan to fit in (i went overboard on mine and put a 6 inch lift in, a 3 inch will work just fine)
A WAY better radiator (Ihad a custom 4 core made)
Electric fan-forget the flex fan crap, and the stock shroud/clutch fan wont work)
Transfer case adaptor
Transmission (ive got a th350)
Electrical splicing, etc (depends on the engine your going to drop in/what you have already)

Jake