Thank you Jeff. The distributor in my engine is part number 1110384 which I can find nothing on... I hooked the timing light up last night and the vacuum advance does give 15° of advance (at the crank) but I think there may be something wrong with the mechanical side of things. I can only make it advance a total of about 11° by 3000 RPM and about 18° by 4500 RPM. Everything I can find says that full mechanical advance should be in the neighborhood of 26 to 28° and as much as 40° for a '67 with a 4bbl
Everything is pretty consistent about 14-15° of vacuum across the year ranges. I guess I'm going to set up the timing map based on the numbers that I can find vs what mine is actually doing. This may be why the Holley computer is trying to pull a lot of fuel out of the map in the cruise area around 3000 RPM. If the mechanical advance is not giving it enough timing in that area, there will be unburned fuel resulting in a rich mixture that the ECU is trying to compensate for by leaning out the map. Thoughts on this?
Here is a shot from a 1969 Motors Manual: