Either transmission will work on any 7M, but they use different flywheels, starters, clutches and are mated with different differentials. The R154 has an inspection panel on the passenger side of the bell housing near the bottom. The W58 has no inspection window at all. The R154 is also a lot larger but unless you've seen both in the past (in which case you probably wouldn't be asking) that info gives you nothing to go on. The W58 won't hold nearly as much power as the R154, up to 350 or 400 if in very good shape.

R154: http://www.cygnusx1.net/Supra/Librar...ection=MT&P=49

W58: http://www.cygnusx1.net/Supra/Librar...Section=MT&P=9

Looking at the diagrams of the two, I. See that the r154 has a plate to expose the clutch setup on both passenger and drivers side. I think I have the r154 since I only looked on the drivers side one. Everything looked real new includind the clutch system which is why I was having doubts that my clutch is sliping. But like u said a lot of things could cause premature whear.

Thanks for the diagrams. Just trying to get a realy nice supra on my streets.
What should I look out for if I change my clutch. Flywheel?