The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Factory part numbers of GMC and Chev T-bars?

Yes, but not in the pickups. It was in the Dubl Duti forward control trucks.
Fourth set is probably for the series 40 (Chevy, 4000 for GMC)trucks. There are a bunch more part numbers for the bigger trucks. 58 and 70 inch as well as some more heavy duty 45 inch rods for the COE trucks.