[CPNE]

To elaborate:

The plywood floor is indeed stock. In panels, it had skid strips like a wood floored truck bed. In burbs it was simple plywood and should have had a rubber mat covering it, matching the floor mat in front. There should also have been a sill plate holding that mat down by your rear doors. Whatever they used for plywood it sure is durable. I've never seen any burb with it rotted out.

As for 3rd seats, the stock rear seat from a blazer is the same as the 3rd seat in a burb, so don't limit your search to burbs only. 3 seat equipped burbs had a shorter second seat to allow access to the 3rd seat. 2 seat burbs had a full length bench for a 2nd seat. If not originally equipped with a 3rd seat you'll need to drill holes after locating a seat. The seatbelts would attach to the seat brackets so you don't have to worry about attaching seatbelts. This is of course if you are going for the stock interior.

As for inner side panels, burbs had vinyl covered stiff cardboard panels attached with a chrome upper trim piece and screws. These were either the verticle pleats for 67/68, or a scroll pattern 69-72, in same color as front inner door panels. The LH side went all the way back, the RH side went to the spare. The spare would have had a vinyl cover over it, in black only.

Hope this helps.