Clarification to Dan's post
He's right about the diesels, with some additional input:The M25XP is a three cylinder engine with 23 hp and a 3 inch heat exchanger.C30s also have its predecessor, the M25, a 21 hp three cylinder. It's essentially the same engine with a 2 inch heat exchanger and a tad smaller bore and stroke or whatever the guts are called, but essentially the same beast. These were installed as late as 1986, most likely for a few years prior to that. We have one on our C34 and it works just fine. Ours is an '86 boat. The M25XP started to be installed in '87 by Catalina.The smaller diesel was a Universal, too, before the M25, maybe 18 hp, maybe raw water cooled, others would know, as would the aforementioned C30 website.