Tim, I have a Delco Remy book that lists a bunch of distributor applications..
An 1112360 lists as fitting a 1950 and 51 GMC 228, 248, 270.
An 1112390 lists as fitting a 1953 228. An 1112391 fits the 248, 270 and 302 of the same year.
The 1112360 has a contact set listed as requiring a D100P or 1944374 and a condensor number D201 or 1900272.
The 1112390 calls for a different numbered contact set, D105P or 1944375 as well as a different condensor, D203 or 1928111.
The cap and rotor part #'s are different as well..
I am not a real student of ignition timing or octane selectors but perhaps you have the wrong set of points in your distributor ??
The D105P could have superceded the D100P and they are one in the same ? Or they could be different parts..
If you want a scan or a fax of these pages, drop me an E mail and let me know.
I am not sure if any of this helps but it's all I got, lol..
