Originally Posted by Locozodiac
Depending on the manufacturer, some sibs/ribs uses short tail engines, better ask the 420 seller/dealer which type of engine is transom recommended before purchasing it
...or check out the Brig website which states that this model requires a short shaft
I wouldn't recommend putting a L/S engine on the back if the manufacture advises S/S - the angle and postion of propulsion will be incorrect and could seriously impact the performance of the craft and possibly the safety of the people on board.
Besides which if you move up to a 4.2m it will feel comparatively sluggish with a 15hp, especially when loaded. Unless it's for river/lake use you'd be better off with a 25-30hp for a 4.2m