Look at the Egge Site. http://www.egge.com/ and click engine kits. Scroll down to GMC, engine kits and click what is in the kit. They are not cheap. I see NOS GMC valves on eBay quite often. Valve guides appear occasionally. You need to be really careful when installing the guides and valves. Quite often you wind up with too little stem clearance and the valves will hang open. I always ream them to the looser end of the specs. That way I don't worry about them seizing.