The T56 is actually a more modern design than the earlier TKs, which use older brass synchro technology. According to the tech guys at Rockland Standard Gear in NY, where I purchaesd my T56, the clearances are much tighter and more critical in the T56, so you cannot run heavier
oil. (Some people have done this as they've had issues with gear whine in the upper ratios, but that is not the fix! Get the transmission "blueprinted" and it'll run silent. Rockland has data on more than 1000 hp being run through the T56s, so they are very strong. The advantage of the six speed on the road is really appreciated. If I were buildiing a car just for track work I might consider the TK as it is lighter, less expensive and shorter, so there is less drive-shaft angularity in a chassis where the engine sits rearward. T56s are excellent transmissions...you just have to make sure the set up is right. Badger