I have a 1964 Buehler Turbocraft with a Gray Marine engine Mod 109 PZ911-l. This number is not published in the Continental parts books. I need to find the Fxxx Mod. number. Any body out there know how to cross reference these. Engine Center in Ferndale Mi. 248-399-0002 said they could get thes valves if I come up with a different no. Rich Warren Mi