 The 1957 Chevrolet and GMC 3100 4×4 price was a bargain at $2549.00 compared to the earlier add on kits.In 1960 NAPCO and GM parted ways when GM redesigned the front suspension on their 1960 pickup line so that it wasn't easily compatible with the existing Power-Pak kits.Prior to 1955 NAPCO Power-Pak conversions were done on 3/4 and one ton GMC and Chevrolet chassis.