You can get the valves at Hughes if you want,
Slant 6 (170-225 c.i. 1960-1987). My machine shop buddy got the valves/seats/springs from his sources and measurements. I would recommend Oregon cams 1206 or 819 for torque/towing. The valves help at higher RPM where the stock head starts to wheeze out, over 3500-4000 RPM.