I second Sandusky's opinion. The A4 has been a great engine in my boat and everything I have heard and experienced regarding Don Moyer is good. I believe he stands behind his rebuilds and parts. If you can't find a good used running A4 you might want to have Don rebuild yours or buy one of his rebuilds. If you want to go cheap but reliable slap a four stroke 9.9 on there. It will look awkward, but they do have there benefits. Unless the boat is going to be a lifetime boat for you I wouldn't suggest a diesel repower. The safety argument against gas is silly to my way of thinking as most of those that argue against it carry
dinghy gas or propane aboard. To my knowledge no one has ever died as a result of an exploding Atomic 4, use your head and the gas will never be a problem.