Some thoughts given the age of the engine and my experience:
My C model had a 72 Factory reman IO-520. It crapped the bed 6 years ago with a lite case and non-VAR crankshaft-the most logical solution was a factory reman. Not sure what the 73 looks like but a R&R with a factory reman is probably $55-60K if not higher if you do a prop IRAN, etc.
As always, pricing one of these is really difficult. A really decent mid time airframe with newer avionics, interior, paint and low to mid time engine is maybe going to bring $125-150K. Dean Siracusa sold a D model recently for $180K ish, but it was pristine I believe. Paint at $20K, interior at $20K, avionics at $50K and engine above is $150K. So, (and not just with a Meyers, but any vintage bird) you will have 2X plus your purchase price for an airplane you might get half ($150 + $80/2= $135K). Which is exactly where I am. I paid $67K for a 1500 hr bird in 2009 and have put interior, engine, avionics (but still a round gauge panel) and other stuff (but no paint) and have $200K+ in a nice airplane that might sell for $135K. So the long and short is you will NOT get your money out of a cheap purchase with significant upgrades.
But they are great birds. And still turn heads on the ramp with that straight tail and 6 cylinder 520…