Vacuum advance adjustment

[JC Mustang]

I received my shiny new vacuum advance control today, and the little bit of paper that came with it says you need to adjust it by turning an allen screw a specified number of turns based upon your distributor ID. Well, my distro says C7DF (I believe...it is caked with gunk and whatever genius decided to put these numbers on the back of the distro deserves to be beaten with a rubber hose...important part is I know it starts C7), which is not listed among the IDs. They are all C8 and newer.

My car is a '68, so apparently it has the "wrong" distributor? I guess the whole engine could be "wrong" since a previous owner replaced the I6 with this 289. What now?

 

[2+2GT]

Well, the adjustment would be essentially the same for a 1968 distributor. What they are giving you, though, is a very imprecise way of adjusting the vacuum advance. Modern "adjustable" vacuum diaphrams are nothing like the originals, which really could be easily replaced. I do distributor timing, and to get it right you really need a controlled vacuum source, to precisely set the curve at varied vacuum levels. "Close enough" won't cut it on this.