What Oil for H...Question on coolant

Also how should you flush the coolant if you cant get the engine plug out? Any recomendations on engine coolant to use?

Have you tried to remove the pipe plug in the block? You can flush the radiator by removing
the lower radiator hose, that would get rid of lot
of crud in the radiator unless the tubes are block. If you're not having a cooling problem,
the tubes are probably ok. I would use a name brand antifreeze. I would try and get that plug out so you can drain the block of that old coolant
and then you would have new antifreeze in the engine and radiator. Use a 50/50 mix and I would change every 2 years. Permanent doesn't mean forever, my late father-in-law thought that's what it meant. Had to have the radiator rodded. Mopar has an antifreeze that is supposed to be good for 5 years, I've never used it since I bought a lot of other brands when it was on sale. Hal