Welcome neilp,
Is that leaf spring bracket riveted on or bolted on? It would be riveted from the factory. If modified it may have been attached with bolts. I dont know the GMCs very well to confirm the configuration, but Bartamos is on the case. It seems to me the bracket should be easy to find in a junk yard. It may be the same part # as the chevy version. Crosscheck the part numbers so it can widen the search. I know of a early-mid 60s gmc that may have that bracket. I hope to get out to that yard in the next month or 2.
