The AC Delco R45 should be a good choice of plug to use.
Does the engine consume an excessive amount of oil?
Is there any blue smoke that comes out the tailpipe? If so is this blue smoke occuring when you first start the engine up for the first few minutes of warming up?
The valve stem seals can be replaced fairly easily. A common indicator is if the engine burns blue smoke when you first start the engine up, then it could be the valve seals.
If you do a compression test and the results show that the piston rings are poor then this leads to a complete overhaul.
Good Luck,
Adam
