If you want an automatic, then the 4R70W is the transmission for you. If you are worried about power handling, then talk with dirtyd0g and/or Darrin about a modified build to handle your power needs. There was a question a few weeks ago about someone wanting to put a 4R100 (E4OD) in one of these cars, but I don't know if they were actually going to try to make it fit or not.
Currently In the Short Bus Garage:
2 - '94 T-bird LX's 4.6L (one with 300,000+ miles and one with 200,000+ miles)
1 - '97 Mark VIII LSC - INTECH V8 (120,000+ miles)
1 - '97 F150 XLT 4x4 Flareside, 4.6L (130,000+ miles) - Currently being dismantled and rebuilt with upgrades!
1 - '00 Mustang GT (likes to accelerate with the brake on!), 4.6L (60,000+ miles - only comes out when I need to get somewhere fast.)