Here is what Pertronix tech sales support has given me in the past (their 2007 catalog is neither complete not totally correct when in comes to early Chevrolet & GMC engines/distributors):
1168, 1168N6, 1168P6, 1168N12 (or, just 1168), 1168P12
The 1168 fits the 1954-1962 distributor cam and is for use on a 12v system.
There is a special part number for use of this distributor cam-size with the standard 1954/55 6v electrical system: 1168N6 (for negative ground, 6v system using the newer distributor) and 1168P6 (for positive ground, 6v system using the newer distributor).
1167, 1167N6 (or, just 1167), 1167P6, 1167N12, 1167P12
The 1167 is for the earlier 1941-1953 216/235 distributor cam and the original 6v system.
The 1167N12 is for an earlier distributor/cam on a vehicle/system that has been converted to 12v negative ground.
