I have played with a few #48s over the years and yes we have found two different combustion chamber volumes. 66ccs and 72ccs. No question about the originality of the heads. The difference is in the depth of the chamber and the scallop on the spark plug side of the chamber. In all my searching and buying I have only found one set of #48s that measured 72 ccs all others measured 66cc. Definitely a difference in the machining operation when produced. If you place one of each side by side you can see the difference. The 48s pictured on my website have the 66cc chamber - about 5ccs due to milling.
Jim
www.racev8s.com