Danny,
I put in the Tremec. I used my existing (small) flywheel, bellhousing, and a stock replacement (for 82-93 Camaro?) 26 spline, 10.5" clutch kit. It runs great. I also went with the Tremec 3550 vice the TKO. The 3550 is rated for 450lb-ft and the TKO for 500lb-ft, I think. It's really fun to drive. The internal rail shifter's really smooth. Some folks also like the Richmond (formerly Doug Nash) 5-speed, too. Fifth gear is not overdrive, though. It has a rod-type shifter, ideal gear spacing, and is based on a Doug Nash tranny designed for heavy-duty/racing use.
On the Forte's GM Tremec, I tried the plate steel Forte's X-member; not only did it flex, but the holes didn't line up. Mike Forte is going to fix it, but I think the TH400 is the way to go. Buy the tranny & yoke, mechanical speedo hookup, and backup light switch from Fortes. Since you don't mind cutting the floor pan a little, get the regular shifter. For the TH-400 Xmember, cut the mount off the back and reweld it in the same location on the front. I don't weld, so I got it done for $20. I had a driveshaft shop shorten and balance my driveshaft ($60 or $80). Do a search, there's a lot of good info on this swap and different opinions. Remember, my car is a convertible for cruising with occasional hot rodding, so I don't always spring for the race/heavy-duty gear. (OK, part of it is that I have four kids and can't afford all of it!) Figure out what you want to do and build towards it. Steve Laabs