I've just done a similar upgrade on my little 1 Ton, '50 GMC 250 with a kit from TSM Manufacturing and it was literally as simple as you describe above. Removed backing plat and drum, bolted on spacer and caliper bracket, then installed C20 brake parts to complete. Installed the same C20 parts on my rear 14 bolt and now have power disc brakes on a 70 year old truck.
