I've done this swap before more than once. The 5.0 is going to be a little slower than your SC but reliability wise it will be fine. What the published #'s don't tell you is that the SC has a much wider power band than the 5.0 which is what makes it more fun to drive. The SC will spin the tires much easier than a 5.0 will.
That being said, a few things you'll want to know before you get started.
1) Anyone can slap a 5.0 into a T-bird, hotwire some stuff, and make it run. However, if you want to do it right you will have some challenges ahead of you.
2) Don't try to use a Mustang motor. Find a T-bird motor. The Mustang motor mounts, exhaust manifolds, intake manifold, accessories, and wiring system are all completely different.
3) Best bet is to find an LX V8 bird and part it out. You'll need lots of little things that just won't be there on your SC.
4) The flywheel on the 5.0 is going to be different. You can't use your SC flywheel. You'll need an 87-96 F150 5spd flywheel and starter.
5) Even when you use the T-bird wiring harness there are going to be some things that are different in the wiring. It may seem "plug and play" but it won't work without some significant changes. Plan on getting the wiring schematics for both cars.
If any of that seems like too much trouble for you then forget the whole thing and find some other solution.