Re: OMC power head swaps (interchangeability of years?)

[Leon]

I would do a full restoration on the 57. Those were actually the best years (55 – 57) for the 10hp. The 5 bolt lower unit held up a lot better, than any other lower unit, on a 10hp. The 58 is a smaller lower unit and the motors weigh a tiny bit less, but those lower units don’t handle "neglect" very well and water intrusion will quickly roast them out. The 54 qd has the same quality lower unit as the 5 bolt, but it is only a 4 bolt and I believe certain parts may not be quite as tough as the 5 bolt. That 5 bolt lower unit was used all the way up to 1973, on motors up to 25hp, so under a 10hp powerhead it wil hold up that much better.

And yes, 51 – 54 are interchangeable
55 – 57 are interchangeable