Yeah, you can beef the T5 up, but most of the hardcore 5.0 folks will tell you it's not really worth it. Searh the 5.0 tech forum for stuff about the T5 and you'll find that there are more than a few posts about stock or near-stock cars blowing the T5 trans on hard use. The thing wasn't originally made to handle the power of a V-8, unfortunately. If you look back at it's history, it was originally designed for the 4-cyl cars. It's a very small trans with small gears. It was later adapted for use in the V-8 cars due to it's light weight and the fact that less power loss is associated with it. But if you're going to be running more than 300hp/300lbs torque through it at the rear wheels, I would say just bite the bullet and start figuring out how to fit a 3550 or TKO into your Falcon's transmission tunnel (especially with 4.11s). Bottom line, I think you'll find a T5 to result in more headaches in the long run, but that's just my $0.02.
Matt