3.8 swap questions

I'm having problems with my 1984 3.8 V6; I'm thinking of swapping out the engine. I can't find a good used 84 Mustang engine. What Ford engines are identical to minimize problems? How can I find out? I'm told the 1984 Cougar is identical. But, I'm not sure. Is this a good idea, will it...

ive been hearing that my 94 mustang's new 98 3.8 V6 will have some computer trouble when i drop the 98 in. true? seeing as its the same generation it should all link up right but i figured id rather double check before i go out and buy it.