Used Intake and Exhaust Valve

I don't know if this will work but, try the magnum valves. The intake is a tad larger but the big gain is in the diameter of the valve stem. You'll need to replace the guides, which is probably a good idea anyway. I'm not sure about the length, maybe someone will chime in here on that. You will have access to chevy valves (alot cheaper) and improve flow on those heads.