The 4 valve twin overhead cam engine is very sophisticated. Putting anything on the head gaskets (or any gaskets) that is not called for in Ford procedures is likely problematic and used to cover up another issue temporarily. Better to fix the engine right when replacing parts. Oil on the plugs will not be caused by a head gasket failure unless it is catastrophic and then you have lots of issues. Is the blue oil smoke continuous?
If the oil is coming from worn rings/piston/cylinder there will be blow-by that can be detected by crankcase pressure at the oil fill cap when opened at idle. The PCV may also need replacing and that could pressurize the crankcase and cause leaks to exterior and onto firing tip of plugs. Replace the PCV anyway and inspect the hoses for leaks. Oil will be burned constantly and worse under acceleration when it may be quite visible.
You can clean the engine with a "Gunk" type product to check for the source of leaks. Pressure washing the engine is not something I would do but others have; manual cleaning is a lot slower but safer.
I will check on the procedure to change valve seals, but it is not likely to be easy. Typically valve seal leaks can be seen on first start-up (after oil has leaked down for a period of time) and again after the throttle is released at speed and then accelerated you will see blue smoke for a short time.
Good luck.
P.S. I have added the basic procedure to replace the valve seals. Note this process uses air pressure in the cylinders to keep the valves from falling into the cylinder.
