idk how widespread (vs only CAP) the vac advance on 68's is apparent on CA Hemis (and other?) chrysler hp cars.
Big write-up here /click
It was common the factory stuff was torn off and lost. In the mid and late1980's anyone obtaining a smog certificate transferring a so equipped car had a kit installed that basically plugged the dist vac port and the mechanical advance had to be relied upon.
p.s. Fuel for thought. If the car was not pieced together and vin swap early on, seems it might not a have been intended a sellable/licensable car when it was reviewed by the press as it had no head-rests. THey became manditory Jan 1 '69.