I replaced a Sole with a Sole after considering the Yanmar option. It's a good motor
and the new models are easy enough to source parts
for (the engines are used by Caterpillar and Mahindra in various forms). The Mitsubishi engine is solid, low revving and is very old school
which to my mind = simple to maintain and repair. The Yanmar is probably better for resale, so this would possibly cancel out the purchase
However, for a DIY
install, a Yanmar is problematic if replacing a non-Yanmar engine. Firstly, they use their own gearbox flange which has dimensions different from everyone else's so the shaft coupler will also need replacing (which can be an exercise in itself and can require shaft removal
for machining the face) and, secondly (iirc), The mounts are lower and closer to the shaft centreline than most other engines - certainly the Sole - which could result in some major engine bed
modifications. There's also the fact that Yanmar DIY
installs are frowned upon to the point you'll need to include an extra boat
buck or two for installation
and the spare part prices enjoy a Volvo-esque reputation.
Perhaps the Betamarine range of engines would be more suitable for your case. The Kubota motor
used is bullet proof and they can maybe provide a unit to the same mounting specifications as the original Sole as an option and this would allow it to drop right in. The only thing they can't do is provide the same connection locations so you need to check that the location of the gearbox lever, exhaust
lines and general protrusions will work
with your engine bay.