The 1947-1954 GMC Maintenance Manual is available from most vendors (as a reprint). If you are searching eBay, you might want to search for GMC Maintenance Manual (GMC did not use the term Shop Manual). I picked up a pretty good original on eBay for under $20, delivered.
Also note that GMC sells separate manuals for different sizes of trucks. The 100-400 manual covers 1/2 ton to 2.5 ton trucks.
The reprint is no worse than the original (I have both) and the reprint can often be better than a shop-worn/dirty/greasy original.
Tim