As we have discussed in other threads before, Chev C8's and C15's tend to draw components from Civvy commercial vehicles much more than other CMP's.
Here we see the rear Chev Torque Tube diff (and some genuine Chev chassis rust).
The diff is sourced from the Chev 1/2 ton truck:
While the instrument panel has been replaced by something equally vintage but civvy, the rest of the Cab interior remains fairly complete and unmodified:
The inside of the left rear corner of the cab has these brackets remaining. The is one in the upper part of the wall that appears to be for a maintenence manual or logbook, but what are the lower ones for?
The wedge shaped one looks like the type used for blades of shovels, but this would only fit a small garden trowel.
Is the felt-padded block with webbing strap a Rifle retainer?