1974 GMC Stepside "Super Custom 1500"

[bbyeater]

Hey guys, this is my first post on this site. My dad has a 1974 GMC stepside Super Custom 1500 .He wants to get more info about the truck. For some reason, every site we go to it can decode the VIN, and that has got us wondering. the VIN is TCZ144Z502401. The truck was olrigianly a 454 Truck. It currently has a 350 with the trubo 400 tranny. When he bought the truck he was told that the rims and tires were olrignal too. However, these are the same rims and tires that were used on the 74 Stingrays. Is it possible this was a special order truck? I have tried to find a 74 Stepside Super custom, and I have only been able to find one. It has the 6 clynder. I have found plently of Long boxes and 2500's.

What does the Super Custom means, is it a trim package? If so what is the difference between the base model and this one.