want2fish,
I hear what you're saying about doing it right the first time. A guy at my father's marina repowered with a brand new engine 2 seasons ago and left the original early '70s OMC outdrive in place. Needless to say, he was off the water right away to repair that ratty old OD after splashing and has had trouble ever since. His reason for keeping it was due to the cutout difference between the OMC and new Merc ODs (he didn't want to do transom work). I bet he's wishing he did it 2 years ago.