Sorry to hear the bad news Adrian, I'd definitely seek a second opinion if you can, low compression might mean it just needs a set of rings, not a full rebuild. I do have a contact who rebuilds cruiser engines, he marinises 1HD-FT's to Yanmar spec for installing into boats and has owned over forty - 60 series over the years. He's in Norfolk though, but maybe could sort you an engine if you didn't want to trailer it down!!?