engine swap

I have a 1984 dodge 3/4 ton 4x4 with a 318 and also have a 1981 dodge 1/2
ton 6 cylinder not 4x4 and want to switch the motors anything wrong or is
it able to be done?

It can be done.

It won't be easy.

Intra-Mopar swaps are always a royal pain in the ass because they
have different bolt patterns,different mount locations, and require in
many cases different crossmembers.

Go to the Mopar dealer and get the performance manual that covers the
swap you want. There always is one. Read it then decide if you want
that much work. Chrysler cost themselves a lot of business from the
hot rodders vis-a-vis Chevy because they were always that way. It's
easier to put a Chevy engine in a Jaguar, or a VW in a Suzuki, than a
Mopar engine in another Mopar.