Russ Martin is definitely knowledgeable and a good source for the nailhead including new and used parts but he is a jerk. He had my daughter in tears and my wife so frustrated when they called to order parts from him for our 425 (we ended up doing research and finding the new parts we wanted directly from the suppliers). But that's behind us now... If you can get past his demeanor EVERYTHING he says is true and worth gold. If you build your own engine and follow his advice you will have a strong, long-living, engine.
The nailhead cam bearings have to be sized to fit the cam - NO new cam will fit without sizing the bearings. This is not something most machine shops are able to do anymore. And do not use FelPro gaskets. The head gaskets will leak oil - another point that Russ makes. BEST gaskets are, like the name implies, the best - and they are what Russ sells too.
I built my daughter's engine; the fifth nailhead I have ever built - They are a great looking and sounding engine, and they make HUGE torque at low RPM. I use TA Performance for parts here in the Phoenix area.