Good luck. I know several people that have done it including a guy that put a DOHC 3.0 from an 89 SHO into a 94 topaz.
No other V6, like from a Taurus, ranger, ect..... will fit directally into a tempo engine bay. You either have to find a v6 donor tempo or spend alot of time retro fitting an engine to fit a Tempo. Then you get to mess with the wiriing. A good chunk of the wiring harness will have to be replaced.
Just to give you a taste, here's something to ponder.