My rule of thumb, keep it simple. If it were mine, i'd pull the oil tank, sump pan an screen. Inspect for debris of any kind, clean. Check timing, points clearances/condition, valve clearances, new spark plugs, clean adjust carbs, etc. Put some fresh oil in sump, tank, cyls, crank with kill button on, then see how it runs. If it runs good, then for riding purposes, lube *all* moving parts. Outside of extreme abuse, neglect the sohc cb750 motors are tough to kill. The bike requires a major service to prepare it for road use. A multi-decade old bike that's been sitting for years should have fresh steering head, swing arm and rear brake pivot grease. Once you've ran it, ridden it a bit, then it will be alot more clear what the bike needs or doesn't need. I realize the bike is an old unmolested gem that you want to give the best of care to; very commendable! Try doing the simple and necessary before going straight out for an engine rebuild. Most likely when the bike was parked it was running fine. Assuming the bike was not sitting outdoors or in a salt bath, little has changed since it was last run. There's no point doing to the bike what it likely does not need. This is just a brief primer on getting a long stored bike road ready. I'm sure you'll get more good advice on this db. The important thing is get oil on all surfaces that have or receive movement !