[rszmjt]

This is a quote from John Hinkley on 403 bellhousing numbers off Camaros.net from 2004 I was involved in-

"The round markers are coded the same way they are on Muncie castings. The large numbers are die-cast mold identifiers."
JohnZ
CRG



FWIW - I have been keeping track of the differences in 403 bellhousings for 20 + years and have found examples where the mold ID numbers range anywhere from 1-9, the difference noted between early and late 403 are as follows -

later issue 403,s (late 69 -72) all seem to have a extra boss on passenger side just above the block dowel hole, but it is not allways just late as some early 403 have this passenger side boss, additionally this boss is also on ALL 403 bellhousings on drivers side location just above dowel also. Sometimes this drivers side boss is tapped to accept the clutch crosshaft ball for 66-72 Corvette and other applications.

Also a lot of the earlier 403 bellhousings (1-6 mold number) have a raised type lip around the pad area where the 403 is cast along with the mold number ( 1-9) and the round month/week date marker. 1-12 for month and 1-5 dots for week.

The GM cast logo is on all bellhousings just above trans and also sometimes it is also on the pad area where the 403 numbers are cast.