new owner rebuild or swap??

hey there, just bought a 87 dodge d50 power ram, reg cab short, the truck runs but they tell me it needs a head gasket. the oil is clean (not milkey) the rad holds good pressure. im not sure if i should just rebuild it or swap a new motor in it. whats the easyist motor swap into these trucks?
thanks for the imput an advice

First off do a compression test on the engine. If all the cylinders are in the same range (not sure of the specs) then the head gasket should be fine.

What is it doing that some one thinks the head gasket is bad?