changing motors on 18' ... problems?

[John R]

If you put a 20" shaft on the same notch your still going to hit the splash well and have your drive too far in the water.

You can replace the transom (big coin), upsize the notch (moderate coin, not best option), or cut the splashwell a bit

[Flatline]

Put a piano hinge in the middle of you aluminum cover and types of locks that slide in a hole and turn down. Sorry I dont know the name. They are kinda like dead bolt locks. When tilting the motor unlock and fold down the cover. Should work fine.