[JayBar]

Not so fast. I have an early BDR #78. I ran a T-5 (from a 6 cylinder mustang) behind a 326 hp (dyno's rear wheel) for a track car and 5 trips to the drags. When my engine went south and I replaced it with a 408 (418 rear wheel hp) I elected to use the tko 600, with the .68 fifth gear. All was well till I ran longer tracks. When you red line 4th and go to 5th the engine bogs. It is not worth the shift for only a few seconds. If I had it to do over again and my BDR was a later model I would most definatly go with the T-56.

This is a great transmission. I have one in my 03 Mustang Cobra (dyno'ed at 448 rear wheel) and it works great. This car is 1,000 lb's heaver than the BDR and no problem.
It gives you the advantage of a tko 600 with a .78 overdrive and one extra gear for crusing.

If you must go with a tko get one with th lower 5 gear. While you may intend to cruse on the highway, after the first year you won't and will be sorry you went with the crusing gears.
So the best compermise is the T56 the best of all worlds.