Swapping out a sick TRS for a Speedmaster III on an old Magnum Raceboat. Can anyone give me a ballpark on how far below the keel I want to locate the propshaft? While the boat is barebones and light for a Magnum it is probalby heavy compared to most modern boats. I will be running around 500 hp initially. I have seen suggestions of everything from 2.5" all the way to 6" in old forums. I have tried to contact the factory to no avail. Any help would be greatly appreciated.

I'd start high, you can always space it down. I'd say about 3" ould be a good start. You are probably gonna have to cut the rub rail area to get the gimble that high.

Better check. I dont think you can use spacers on an early SSM III.