SST45 uses the same powerhead as the T750 OMC. Under T750 rules you can run the SST45 tuner. You cannot run the SST45 lower unit. But, you can put on a nose cone or run the SST60 gear case. S750 is a T750 motor on a 12 to 14 foot non celled tunnel. APBA had TWO classes similar to S750......one was Formula 50 [a Wayne Worthy class] and the other was Fat C [a Ron Hill class]. Our OMC T750's are very strong in our group. They were not strong in Formula 50, even though stock outboard found they TOO strong for their D classes and do not allow the motor in the classes.
Interesting video:
https://www.youtube.com/watch?v=wGzLnzICZcg&t=45s