Have come across a omc 230 in a 20 or so foot imp walk through bow rider. Think to be 70's or possibly early 80's. say it has been under cover or dry storage up until last year. interior good no rips, hull could use some work, new rub rails and such They say the first time out took on water (freeze plugs leaking) second time out ran fine. Third time found water in oil. want to get rid of cheap, talking about cutting up and throwing away. Would have to talk them into selling trailor. Know little about I/O. do have experience w automotive. Will a gm 305 or 350 have the same block and heads for a straight up swap? If so, do believe i will upgrade to this old bow rider. Thx in advance