Allen, yes the AAR Lola T.70 used the heads first ( in the MK II version ) with success in 1966 as well as the MK I version (of the head) and the MK III version, perhaps for fuel injection ,was used in the 1966 Eagle.
I know this because I just got the new book on Gurney Eagles. The Gurney heads were just a part of the system he used. He says he revved the engine over 9000 during the Bridgehampton Can Am race in 1966, which he won.
I do not know any particulars about the system for distributing the heads amongst the teams though. Interestingly, Team Surtees tried Weslake heads on their Chevy Can am Lola in 1969, but to no avail as McLaren came out with the Reynolds Aluminum BBC.
Regards,
Johan