Re-Powering the Legendary Contessa

That article is a little lean on content :-(

I am surprised you rejected Yanmar as the 1GM10 is still available and is pretty much the default option over here for C026es and anything else in the 22' to 27' range.  The main limiting factor is the width of the engine across the aft mounts.  Their interaction with the curve of the hull means there is a big tradeoff between shaft angle and protrusion into the cabin.  If you fit after-market mounts from R&D couplings, you get a 1/2" reduction in height + the mounts are available with shields to protect against stray oil and diesel + they are captive mounts that do not need safety wiring.  The price of the R&D mounts is approximately 1/4 the price of the Yanmar ones so you should be able to resell the unused Yanmar ones and make a profit on the deal.  'toe in' the rear mounts and invert the air filter mounting plate to let you mount the engine a few inches further aft and the amount of engine box rebuilding required should be fairly minimal.

I was hoping for something interesting like building a template with a sheet of ply for the mounting plane of the engine and coupling face, complete with bolt circle and blocks of wood + allthread to mock up the mounts and polystyrene blocks to mock up the rest of the volume it takes, then bolting it up to the shaft and sliding it back and forward while checking clearances on the hull and joinery or mounting a laser pointer inline with the coupling center and checking alignment that way.

How much of the work did you actually do yourself?

Stripping and rebuilding your Farymann to factory specs would almost certainly have cured its misbehaviours which may have been due to low compression + either fuel starvation or some temperature related problem.  If you stripped it and inspected all the parts BEFORE ordering any spares, you would have known whether it was worth doing and only been out the cost of the workshop manual.

I rebuilt my over 20 year old 1GM10 a few winters ago.  Total bill for the engine came to approx 1/4 the cost of a new installation though I didn't do the gearbox.  90% of the work I did myself, using specialists for the crankshaft regrinding and injector reconditioning, but for final assembly and testing I did a deal to use a bench at my tame auto mechanic so I could use some of his specialised tools and have experienced assistance with some of the trickier bits like getting the timing case back on with the linkages properly engaged.

I guess it all depends how 'hands on' you are willing to get.  If you have lots of money and are never going to cruise remote areas, you can just ask the yard to re-engine your boat, but if you don't mind getting your hands dirty, and aren't a danger to yourself and others if in sight of a toolbox, and are capable of reading a service manual +  stopping to ask advice if you aren't sure rather than bulling on "Git 'er done!" till you break something expensive, being your own small diesel mechanic is something most yacht owners can do.  The payoff  is the first time you fix your own or a friend's engine in a remote harbour, with no local mechanic or one who "No hablo Inglés".