There's not much room in those engine compartments. If you want to clean and paint it the engine needs to come out. If there's any question at all about the health of the block you are better off tearing it apart and making sure. You don't want to be throwing money at something that's got serious problems. There are plenty of 390's out there if yours is too far gone. If it turns out to be good then you'll get a good education in rebuilding FE motors. If you search through past threads you'll find some that deal with improving the oiling system. I'm sure Dave has some tips that you can do to improve on the design.