RE: Welcome to Club SAITO !
Most of the 150's are the same. The very first one had a very high compression but it would have an "A" stamped on top of the right mounting lug. The first engine's muffler has a bunch of little holes for the outlet.
The 150AAC 150S and 150H are all the same thing.
Saito originally called them the 150S. For some reason, Horizon refers to them as the 150H. All 150's are of AAC construction.