Stuck Whizzer Valve
Traveler,
Just reverse the procedure for the IN side, i.e., if the EX valve is on the opening ramp it's fine to tap the IN valve. The IN valve would typically be even easier to free than the EX valve since there is less carbon build-up and corrosion present in the much cooler running IN guide. They are usually not stuck very tight, and any motion tends to loosen them easily (probably a light tap with a plastic screwdriver handle would free it up). Use any low viscosity petroleum penetrant you want. You will not hurt anything by tapping the valve head squarely. The truth of the matter is there is a better than even chance that the guides and the valves are junk anyway, so don't fret about it. This is a very non-critical undertaking. Lube it, tap it, work it, and it will be free. I've seen several Whizzer barn jobs with stuck valves, that with a little lube and tapping, started right up.
Look on the engine case near the oil drain plug to see the model/serial number and let us know what you've got there (probability suggests you have a model H, but you never know).