1957 Chevy Suburban 4x4

[gcm]

Just curious how rare are chevy suburban 4x4s, now I know i haven't seen one in person and this guy claims to have one sent me the VIN and I'll call the chevy heritage center to confirm it's real. Now he claims it's a factory chevy 4x4...from what little I know 1956 chevy 4x4 was a napco add on that was added by the dealer but 1957 onwards it was a napco system added in factory by chevy, right?

He claims it's the original drive train and it drives and runs so really wanted to know what you guys think.

Thanks