We have a 1979 CT41 ketch
that came with a 75 hp MD21A Volvo Penta
engine. It ran well (except for having to replace the fuel
injection pump - twice - due to fine rust from the black iron fuel tanks
making it through the filters into the engine. We replaced the engine.......not because of the injection pump......though that was difficult enough, but because when the fresh water
pump started leaking....we couldn't get parts
. Anywhere. And as we worked to remove it, bolts kept breaking. Too much corrosion
We replaced it with a Yanmar
. Replacing an engine is such a pain......I can't imagine in your case that another, used, Volvo, was used.
Consider the possibility (likelihood) that you'll have to replace the engine, and check out the fuel tanks
. Ours were under the settees, relatively easily removed, and we had replacements
made of aluminum
It can be done. If you love the boat..........