351w

When I put the 351W in my '66 Ranchero which had a 289 in it from the factory, it was pretty much a drop in. The block is taller than the 289/302 block. If that '96 V6 is a 4.3 look carefully at the motor mounts they might be the same since the 4.3 was basically a bobbed 302/5.0. Cleveland heads flow a ton. Boss 302 .. Cleveland heads. From my early in life Ford experience.
Unfortunately the engine in there now is a 4 cyl. And the mustang is the 3.8, so neither would be a drop in fit. I got the ranger for basically free, and it gets driven daily with the current engine and 5 speed manual transmission. But has 240,000 miles on it, so eventually it is going to give up. I also have a 4 cylinder perkins diesel that I picked up for $100 that was out of an '84 ranger. That may go into a little rock crawler project. But that's another day.