I doubt whether gmpartsdirect will have them. However, I have a "Truck Parts Catalog" dated Sept 73 which covers Chevrolet 1946-72, Series 10, 20 and 30 - it is "P&A 31". Paid about 60 bucks for it on ebay. Good to check some of the literature vendors to be found in Hemmings Motor news, too.
My "Chassis Overhaul Manual" is "ST 333 71". Shop manual is with the body, not here in my office.
I think you can get reprints of shop and overhaul manuals through the truck parts dealers such as Chevy Duty at about 50 bucks or so. May be able to find CD versions also, but I prefer a book.
Good luck
JB