The 3.0L may not be a powerhouse, but it'll outlast the sun properly maintained. The only weak spot you've got is the AXOD, but with some preventive maintenance, you can keep it going.
I'd recommend regular ATF fluid changes about every 20K miles with Mercon V and adding a external transmission cooler. The transmission definitely runs a bit hotter than is useful naturally, which breaks down the fluid. If you do the above, you'll get plenty of miles out of it.
There's a member around here, Double Negative I believe, that had TecNickal's old '87 Taurus wagon that got five speed swapped, but I forget what the donor transmission was from. I do recall it could still chirp tires going into second though.