[quest]

Well it depends on the year, my one ton GMC is either a 64 or 65 and is a 930 however my 65 3/4 ton 4x4 is a K92534 and the original badge on the cowl says GMC920.
(1 of only 57 built of my model in 1965).
When ever I try to search parts online with U.S. vendors I get the most results searching Chev K20 but GMC K20 gets poor results.
I ordered my original documentation from GM vintage vehicle services in Oshawa Ontario and they also sent me a photocopy of the GM Truck specifications manual for 4x2 & 4x4 pickups, panels, suburbans, cab & chassis, vans. This book lists Chev or GMC 4x2's as C10, C20, C30 and 4x4's as K10, K20 but of course there is no K30.
Then it has several pages on standard spec for each and all the optionals specs. It has a section on all the optional engines, all the available truck configurations, transmissions, diffs etc.