Re: 1973 volvo penta 270 glastron v174 leaking missing winter plug??
Compression spec is 170 to 200 lbs. Be aware that readings on an engine that has been sitting can be low due to rusty valve seats, glazed cylinder walls, leaky valve guides, or other things. Compression MIGHT come up after running it at temp several times as rings seat and valves settle in so don't get too dissapointed if readings are initially low.
Keep in mind that you're dealing with a lot of unknowns so all of the routine maintenance items like tuneup, engine and outdrive oil changes, impeller replacement, and lube of moving joints and bearings are in order. It's a really good idea to build or buy an outdrive pressure and vacuum tester so you can do those tests.
Pulling the upper gearbox after the tests is also recommended so you can check the condtion of the u-joints and bellows. These are normal maintenance items and will save big money if you identify and resolve problems before the parts fail.