[Coley]

Where did you get that VIn number from?
As demian said....check the 'SPID', which is the info/option list on the inside surface of your glovebox....hopefully it is still there, intact and readable.
It has the VIN on it and that should match the stamped VIN on the riveted plate within the drivers door frame.

As for the rear leafs, back then GMC standardized on having 'rear leaf' suspension as the standard suspension...with trailing arm/coil as an ordered option only.
Chevy was the other way around...they standardized on having 'coil' rear suspension with 'rear leaf' as an ordered option.
Your truck having leafs is pretty common on GMC's and if you plan to haul anything it is a better choice.

If you get a chance post up a few pics...including pics of that (inner glovebox) SPID sheet....and we will be able to help you out more.

Welcome.
Coley