I don’t know about after market disk kits but I did have a similar experience with my ½ ton 67. I replace the brakes with 72 ½ ton disks. My stock 67 rims did not fit. I replaced the stock 5 ½ x 15” wheels with stock 6 x 15” wheels found on 4 wheel drive 71 and older four wheel drive chevy trucks. Look stock and work great.