I spent 50 years building cars from the frame up and if I did not see any leaks after cleaning the housing, I drained the axle and replaced the 80-90 with newer fluid, drove it around the block a few times to circulate it, then checked for leaks again. The seals and banjo housing (3rd member) are the places to check. ALWAYS rebuild the brakes on a car that has sat for over a couple of years. I pulled the plugs and shot a little oil in each hole, then spun the engine with the starter. If it turned okay, I cleaned/checked the plugs then installed them. Make sure the oil level is okay with NEW oil before turning over. Replace the oil filter, and check the points...it is a 68, right? Look for any leaks where parts join (heads, intake, exhaust, etc.) and remove the valve covers. If sludge is everywhere and it smells like burned oil, TEAR IT DOWN! Depending on mileage, a good cleaning with new fluids may fix it. Just removing the head may expose a lot about the engine. If no deep top-grove (where the rings top-out) that catches your fingernail when dragging over the grove, you are good-to-go. Some say to run engine cleaner in the oil, but only for a few minutes to remove sludge build-up. I prefer to look inside with the head and pan off. No need to rebuild if things look good, just clean things up, replace fluids, adjust tunable parts to factory specs, and drive it. Sitting is bad for any car/motor, so think about what happens when not driven. Grease, oil, water, trans fluid, brake fluid, fuel, electrical current...does not circulate. Just stop and think. It has been a while but I come from a poor family and have owned many used cars. My Dad and older brother were machinists and understood metal surfaces and wear. They showed me what to do and it worked for me.