My FIL has a aluminum rivet hull that basically is my son's whenever he wants it. I think it's 14x42. Can I just buy a small SD mud motor and put it on it? I just need it to get through grass in the lakes and don't plan to do much mudd'n with it. What kind of bracing should I look at doing. What size would be too much for this hull?

Lake Bouef has so much grass that a OB is put through too much.

The Mudmotors put MASSIVE strain on the stern of a boat. With that said, you will have to make sure that the Transom Gussets are big enough. Also, you will probaly need some sort of brace from the Stern to the bottom of the boat.

On a 14' boat, a 23hp would be plenty big enough.