Re: johson super seahorse 33 model
For what you need, I really think you would be OK with parts from any of the 33hp model years.
As F_R correctly pointed out to me not long ago, there are some parts differences between the 28hp motors and the 33hp motors (they are essentially the same motor and share many parts), but when it comes to stuff like impellers and drive shaft o-rings, my bet is that there aren't any substantial differences. Since I have been wrong before, however, just verify this from whatever parts source you go to - they should be able to tell you quite easily.
One thing you might pay attention to, though, is difference in complete water pump kits. For example, the OMC 6hp motors can have "small" impellers or "large" ones - it just depends on which kit your get. The difference is in the size of the cup in the pump cap. The last time I ordered an impeller for one, I forgot about this and ended up with the wrong size for the pump cap/cup that I had. No big deal, because I just decided to bring the impeller back as an individual item and buy a whole kit, which is what I probably should have done in the first place.
I'm not sure that this is an issue with the 33hp motor, but its a good thing to keep in mind.
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