Beta (which are simply marinized Kubotas, from what I understand) have been getting good reports not just as a drop-in for Atomic 4s, but generally as reliable small diesels that are a shade more intelligently designed, particularly for the typical "lift off the companionway stairs" access option.
I never thought I would appreciate having an engine bay I can simply stand in, but I do, as the thought of hauling my engine anywhere but directly up is fairly depressing.
I think it's a shame that the "engine box in saloon" style has pretty well disappeared. I'm sure modern soundproofing techniques, careful venting, and other methods could make it work. Having the diesel in the middle of the boat not only makes sense (360 degree access), but puts the weight over the keel and closer to the CG. It also means the shaft and prop can exit the boat at a shallower and more useful angle.
But I digress.