In the process of repowering myself
I am in the process of repowering my 78 H30 w/ YSM-12 as well. As you have observed, the 2GM20 will fit in the rather large engine box with no problem. The engine mounts on the 2GM are ~2" closer together side to side than the YSM, so modifications to the bed rails may be necessary. You may also need to add some spacers under the mounts to match up the output flange to the prop shaft. I don't have that dimension for the GM, but the YSM flange is on center with the mounting brackets on the engine (about 2.5" above the bed rails). You didn't indicate it was the 2GM20F (fresh water cooled), but that would certainly be preferred. I looked into a rebuilt 2GM20F for my repower, and also missed out on a couple of E-bay very low hour engines. I ended up ordering a Phasor P3-20-SM just today. Phasor is primarily known for Diesel powered generators using Kubota engines, but they also marinize the Kubotas for propulsion. This is the same base wengine as the Beta 20. I looked at all of the engine companies at the Annapolis show and the Phasor appeared to be as well marinized as any of the others (Beta, Nanni, Vetus, Universal, etc.) They were the most competitively priced, hence the selection. This engine fits easily in the H30, w/ mouont spacing equal to the YSM, but I will have to build the rails up ~2" (beats, having to lower them). I figure once I sell the YSM, I may have an extra $1200 invested for this engine as opposed to the rebuilt 2GM20F I was contemplating, with ~40 lbs less weight and readily available Kubota spares. I am taking the opportunity of the repower to improve the engine enclosure, improve the galley cabinets, relocate the batteries, and replace the fuel tank (I don't want to think about what is in the bottom of that tank after nearly 30 years). I have a tentative prop size from Campbell Sailor for a 13x7 RH 3-blade, but have not ordered yet. I want to have the boat hauled next week and get the clearances to see what other options I have for props. Your 2GM is a RH rotation also, so you will have to replace your prop as well. I told the guy at Phasor that I am anxious to have an engine that isn't old enough to have voted in the last 3 presidential elections. I don't think I'll miss the rumble of the Yammerin' Yanmar, but it has been a reliable engine. The link is for the Phasor site in case anyone is interested. Good luck with your project.
