If your gauge is accurate, I think you are due to replace the bearings at a minimum. If you have 12# driving and it increases to 20# when you let up on it, your main bearings are loose. Those little Chevies very rarely give any crankshaft trouble, but anything is possible. You probably could get by with just new bearings. Of course, you won't know until you tear it down.
Also, on the loose nuts on the valve train, you can simply take the nut off and strike it with a hammer to make it tight again.
