Ok, let's try this again. I go slower. Since you have a car on the same chassis as a Mark VIII, get rid of your V6 and swap it for the Mark VIII's 32V Intech V8, that one does have 290 hp. You find yourself a Mustang V8's transmission, the T56 6 speed manual and put those 2 together with the proper wiring harness and chip. Hell, when all said and done, it's gonna weigh as much as a Supra anyways, but with V8 power. So while you're at it, convert the rear drums to disc's, courtesy of that said Mark VIII. And when you're tired of shitting on these little 4 bangers on the highway, Turbo it at 7 psi, you'll be making more power than any other said car due to the amount of power you'll have from the start. You don't need to get a supercharged car just to have a 5 speed. It's all about going custom. Check out these links.
http://forums.tccoa.com
http://forums.tccoa.com/showthread.php?t=97219
http://www.cardomain.com/MakeModel/Ford/Thunderbird