John : I may be able to help some here, or add to the confusion if nothing else. First, stating with the bottom photo : For the Brass fitting, we can rule out it being the C6AZ . I say this based on the "Vacuum Fittings" chart from Osborne's reproduction 1967 Mustang Chassis Assembly Manual, and the pictures that follow of an NOS C6AZ-A fitting. Note that the C6AZ only has 2 nipples on it, while the one you pictured has a third nipple at 90o to the other 2. The one with the 3 nipples that you show is apparently the C8 one (see page from Mannel's book, referenced later). However, to add to the confusion here is that in the 1966, 1967, 1960-68 and 1965-72 MPC's, the C6AZ-9A474-A is show for 6 cylinder applications, while the C6AZ-9A474-B is shown for 8 cylinder applications. The description of the "-A" and "-B" is identical in all of the MPC's. Unfortunately, I do not have an NOS C6AZ-B to compare. My thoughts were that the difference could be that on the "-B" the 2 nipples were the same size (as I have seen fittings that look identical to the "-A" except for that, although not on a 65-67 289 or 390), but that would mean that the picture previously mentioned from Mannel's book is incorrect. Possible, but doubtful. In any case, there wouldn't really be any difference in using either one as they would of course function the same.
I did check my OSI catalogs to see if the "-A" was ever replaced by the "-B", or vice versa, and no, that did not occur. As a matter of fact, both the "-A" and "-B" were available until sometime between January 1983 and January 1987, when they were both finally shown as "NR".
On the vacuum tree shown attached to the C6AZ fitting, that has me puzzled. In all of the MPC's previously noted, plus the 1973-77 and the 1980-89, T could find no description of a vacuum tree with external 3/8-18 threads on both ends (although the descriptions in the 73-77 and 80-89 are not near as detailed as the earlier ones). So, I don't have a clue what this tree is for.
Now for your first picture. This is a little baffling too. The vacuum tree appears to have a heater hose type elbow attached on top, which makes one think that the vacuum tree might be a distributor advance control tee, yet there is no temperature bulb. Thus, possibly this elbow was used in place of a flared fitting and tubing for an accessory ? As for the vacuum tree itself, it appears that it may be one of the "variations" that Bob Mannel noted in his discussion on 1968 Vacuum fittings. I have attached copies of the appropriate pages from his book (“Used with permission by Bob Mannel”). Of course, no Part Numbers are noted.
That's about all I can add to the discussion. Unfortunately, it doesn't really answer your question about Part Numbers. I think the only sure way to find that answer is to find these that are NOS and in the package.
Bob
