Need help dating a GM bellhousing

My friend has a 4 speed (I think its a Saginaw) manual transmission for a small block Chevy. The bellhousing is missing the lower dust cover and the rubber boot for the clutch fork. No parts store can get him the proper covers without knowing what year of vehicle the bellhousing came from. There are several numbers cast into the housing on the mating surface for the transmission:

GM1, 3836923, and E275

I've tried searching around, but haven't been able to find anything on these numbers. I have yet to see the part in person, as my friend read the numbers to me over the phone. Does anyone know how to read any of that? Or perhaps there is a date code somewhere else on it that he overlooked?

Well, he found another number on it that dates it to a 1957 6 cylinder truck engine.