When you say valve stem seals, did you actually measure the fit of the valve to the guide? Knurling them will fix the problem for a few miles - maybe, but replacing the guide is the only sure repair. Fords are notorious for wear and just replacing the seals will not cure the problem. These engines are not friendly to work on with that monster intake that is actually is part of the head. Gaskets easily move or are damaged - then oil consumption and/or vacuum leaks. Often you can hear hissing or see excessive oil fill tube vapor if a gasket is a cause