I think I'd go at it this way:
1. Get a full gasket kit and head seal pucks (PartsNmore has the pucks, I think).
2. Take the engine out, and pull off that top end. At this point, no matter what you choose to do, the 14 years of sitting will result in a bunch of oil leaks after it runs a while (I haven't seen that fail, yet!).
3. Figure out what size pistons those are: if they are stock and the miles are low, and the bores not rusted, you can get new rings on eBay (look for Mrssuperdeals, MC rings) for about $30. Or, get some oversize pistons if the bores are damaged, or for a more complete job of it, but then it will have to be bored to fit them. That will probably cost about $200 in machine shop work, if I understand California's machine shops...
4. Take out those valves and spin them in a drill, polish off that rust with crocus cloth or 600 grit sandpaper and see how they look afterward. They might be OK. New ones are about $10 each at VintageCB750.
5. Most important on the "F" bikes: you'll have to check the clearance on the (at least) exhaust valve's guides. We can talk about that when you get there...this is the highest-wear part in all of the 750 engines, beginning in 1976.
6. Pull out the clutch plates and soak them in oil at least overnight. This will prevent damage to them when you go to start it up again. Otherwise, they are now so dry that the first time they slip against each other they will damage their cork faces, as they have conformed to the tiny dimples in the steel pressure plates. Soaking them will mitigate this problem and probably save the clutch.
And go from there?
