I don't understand "My 2403". Is that a number from a distributor? Below is a page from 1955.2-1960 GMC Master Parts Book listing all distributors used in GMC gasoline engines. The only one used in 302 engines was 1112414 which replaced 1112411. So same weights and springs 248, 270 and 302.
The same book shows vacuum advance units used on 100 series (1/2 ton) thru 300 series (2 ton) and some 340 series trucks. Larger trucks did not use a vacuum advance unit.
Vacuum advance units may provide better gas mileage and maybe cooler running in high vacuum situations. Big trucks didn't use them because they were mostly driven pedal to the metal.
I have a mid 50's Chevy high cap distributor in my GMC 228 and I plan to use it in my 302 if I ever get it running and installed.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
