Probably because he'd need a new trans, wiring harness, exhaust, computer, and everything else connected to the engine to do either of those swaps. He'd basically have to get a donor vehicle. Not to mention the time required to get an engine swap fully functional. Or he could spend a weekend, and several hundred if not thousands of dollars less and just put another 3.0 engine in.
To answer the OP's question, yes it will fit. It will be much easier if you keep your upper intake manifold, and everything upstream from it (throttle body, intake tubing, etc), as well as the exhaust. Your truck also has a cam position sensor, and I believe pre 95 3.0's had a distributor, so you'll need to keep your CPS as well, or preferably, replace your current CPS with a new Motorcraft part.