Is your manual the GMC SM318 book, or something else? I have a PDF of the GMC SM318 Unit Overhaul Manual (1955.2 Series and later open drive version) which I could email you if you like. The main case components are the same for your earlier SM318 closed driveline version. Can't remember where I found it on line many years ago, but can't seem to find it available for download anymore.
I've found that GMC Manuals seem to be better detailed than many of the corresponding Chevy books, even though they share the basic same design and parts for the most part.
Let me know if interested in the PDF.
