Re: Cutting the Transom - HELP!
Why don't you just build on a set back plate and leave the transom at 20 inches. That way, if in the future you do get a 20 inch shaft engine, you don't need to rebuild it.
The tiller arm should still be high enough to clear the transom, even with the engine set down 5 inches behind it.
At any rate, most hulls run best with the cavitation plate even with the bottom to about one inch above and as long as the intakes are covered, the engine will still draw cooling water.
BTW: Over on the OMC forum there was a post: Those guys seeking maximum performance without a nose cone, surface running prop, and low water intake, glue or weld shut the top one or two intake holes so they don't suck air with the engine set very high. The engine still gets enough water to cool it through the remaining intake holes.
