Dave : Thanks for adding the picture of the C6AZ Spacer. Not having a '67 390, that should help a lot. I agree, there is no way that nipple is large enough for the hose to the PCV valve. That being the case, and that the same spacer is shown for all applications, I was going to note that caps must be required to plug it off in non Automatic Transmission applications. But, you beat me to the draw and covered that in your next reply - Good job !
I went back and looked at my 3 MPC's, and while the caps don't show up in my January 1967 MPC, if I would have looked on down to the bottom in my 1960-68 MPC (page dated June 1968) and at the bottom of my 1965-72 MPC (dated 1975), there they are. My bad.
This is another good reason why more than one set of eyes can be very helpful.
Preaction - sorry if I jumped to conclusions and misled you.
Also, no, the Casting Number for the Spacer did not come from any of (at least my) MPC's, but from the "list of Casting Numbers that I previously referred to.
Thanks again Dave, for coming in on this.
Bob