No, the 3550 does not come in GT's or Mach 1's. There are 4 basic variants of this transmission. Standard, Standard II, TKO, TKO II. The TKO versions can handle more torque. The II versions have a non-overdrive 5th gear (.68 instead of .82). This is all really moot now as the 3550 series has been discontinued. It has been replaced by the TKO 500 and TKO 600. The 500 is only available with 3.27 1st and a .68 5th gear. The 600 is available with a 2.87 1st and either .82 or .64 5th gear.

The 3650 comes in the mid 01+ (i think.. may have been 00) GT's and 99-01 cobra's and mach 1's. The 3650 has an integral bellhousing that fits the modular motors.

The T45 was available in 4.6L GT's up until mid 01 and cobras through 98.