As previously mentioned, the only way a Chevy store could order the Z-11 parts was to have the info from one of the cars, serial number, selling dealer, delivery date, etc. That info was then called in to the Chevy Parts Depot where one of the guys there that handled off line stuff would verify the info and then place the order. All of the parts came from the Chevy National Parts Depot in Michigan and were strictly controlled. They would ship immediately any part requested with the correct info. Now, as soon as any Chevy store got the info the first time it was "game on", they then could order anything for anybody. One of the limiting factors was the price. I believe a bare head listed for $115 and I believe dealer cost was $96 in 1963, so that is about $900/800, list/cost, today per head. Then you had to buy, valves, rocker arms, push rods, push rod guide plates, short block, pan, even the fuel pump push rod was different(titanium), intake, valley cover, gaskets and on and on. By the time everything was added up I remember specifically it was staggering at that time. Don't forget that the 396/427 was starting to be rumored by that time with the appearance of the Mystery Motor at Daytona. While we had several guys wanting the parts we ordered them and they ran the stuff through out the 63-66 period. After all we had nothing else to compete with. I for one had to lighten everything on the engine to get it to be a high rev engine because it already had all the torque it needed. I had to lighten pistons, crank, valves, valve spring retainers, etc, this got me to 7500 RPM in 64 which allowed me to blow up things much faster!!!
All in all, while a few people were able to get the "over the counter parts", Chevy made it very hard to get. Many times we were told they were out of production, get over it. However, if you persevered, pestered them, go over the local guys heads to Michigan you could get a few pieces. Bernie Krauss was one of the best guys with Chevy in Detroit, if you could get to him you could get your parts. I have a Z-11 intake with a casting date of 1965, so I know they made a few parts through then.
Bottom line Chevy top execs decided to kill racing and threatened everyone that supported it, so it made it easier to just not fill orders as time progressed. They agreed to fill some orders based on who you were and that was about it. I used Haydens info to get parts for several years, but Chevy knew guys like Hayden and others had to switch to other brands to race so the pressure for replacement parts was not going to be great going forward. Many others will have an idea about how many heads etc were made, but I would bet not many given as hard to get as they were. I know I had mine welded so many times they looked like welding school rejects. Anyway thats what we did.