I found a used Beta 14 that sank during the repower - not that the previous owner disclosed the sinking part.
Had that not come along, I would have rebuilt the MD7a and put a heat exchanger in it, but I might be uniquely qualified to do that being a mechanical engineer and former auto mechanic. You can follow the saga on the first link in my signature if you are interested. Here is a video of the MD7a just before I removed it. I'd be interested to know how yours compares. YouTube - MD7A running in boat