about two years ago i picked up a 56 gmc 270 for the ashton that i didnt use but its now going into my 40. the carb that was on it was a rochester which didnt come with it originally but it worked. since i had a zenith to put on the 270 i had the carb rebuilt and had it as a spare. when i got my 51 6100 dump with the original 235 engine the carb(rochester) was messed up so i went to put the rebuilt one on the dump and it didnt match the stud spacing on the intake and it confused me and i put it back on the shelf.

fast forward to today, i picked up a 59 235 a couple of weeks that so far looks promising to replace the 51 235. the 59 carb looks like it needs work so when i go to test run it i thought id use the rebuilt rochester. i removed the 59 carb and went to put on the rebuilt one and it doesnt match the stud spacing. looking at the bottom of the throttle body the rebuilt one's bore is much smaller than the one from the 59. everything else on the exterior of the carbs is identical. when did the stud spacings change and what application was this narrower stud spacing carb for?

40 GMC 250 STAKE/FLAT BED
1951 Chevy 6100 Dump
51 GMC 350 ENGINE 500/500
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