[Rick Parker]

AZFORDMAN:
The overall limit can be changed. The distributor must basically be disassembled. The round part that the rotor slips onto has the mechanical advance mechanism attached to it under the base plate. It has 2 slots, one that may permit 16 crank degrees and another that will allow for instance, 24 crank degrees, the number of available degrees is limited by the length of the chosen slot and the pin that limits its travel. That number plus the intial (18??) is the total advance you will have available. The distance the slots allow can be altered by reducing the length of the slot. (Heliarc works nicely.)
To disassemble it, carefully remove the small wire clip in the center under the rotor, remove the c clips on the vacuume advance mechanism, remove the reluctor without breaking any of the tangs, then remove the baseplate. At that point the mechanical advance will be visable. The distributor bodies are pretty much the same between an electronic as pictured and a point type ignition.

The calibration is best done by someone with access to a Distributor machine.