I just got a tractor at auction, it was advertised with approx 100 hrs. on rebuild and water in the oil. The tractor is a 1968 Case gas 580ck and from all appearances the block has been out of the tractor. When I filled the radiator to test run I could hear the water running into the crankcase. I cut the radiator hose and filled the block with water and it appears to hold water up to the top of the block. What are the chances I'm lucky and just need a head gasket? When I went to do a compression test I discovered that neither set of threads on my tester were large enough. Pulling the head doesn't look to be too bad of a job, should I spend the time on a compression test or just go on and yank the head off?