I've read online somewhere 1978 was the last year GM designed the rear of the Suburbans to accept either barn doors,or a tailgate,simply by bolting them on,all the hinge mounts were there,and the floors were the same.....after that they changed the floor/sill area ,making a swap to barn doors not impossible--but requiring some decent bodyworking skills ,along with said section of the donor barn door-ed Suburban to graft into a "tailgate" Burb...
When I first bought my '85 Suburban,the fact it had a tail gate was a bit of a bummer,I prefer barn doors,loved them on my van--no power window to malfunction,no rattles,risks of busted glass,etc..
I was shocked to stumble across a pair of barn doors on a 80's burb the same color scheme as mine in a nearby salvage yard--I got the pair for 65 bucks because they had a bit of surface rust and pits--I removed every bolt,hinge,etc,and kept all the hardware...I was stoked!.
While I was stripping these parts,a worker was impatiently waiting in a forkloader,to scoop up the Burb and load it on a flatbed that was to haul it to the crusher..I picked THE day they decided to "crush out" many of the old vehicles to gain room..

..had I waited a day longer,it would have been scrapped already...
The guy who owns the yard told me he doubted I could just bolt on the barn doors,he didn't have an old Hollander interchange catalog that far back any more,but he was pretty sure GM changed things around 1978....and I asked if I could return them if they didn't pan out--he said he'd give me 50 bucks back (and he rarely does that for anyone)--or I'd get "yard credit" for some other parts in exchange..
Unfortunately he was right,I quickly saw the rear floor area on my burb was way different when I got home,and it lacked the spot for the hinges to bolt too also..(which would not have prevented me from welding them on,but when I saw the hassles involved modifying the floor,I said "screw that"--especially since the donor truck was already squished probably.

--.and I brought the too good to be true doors back and got my 50 bucks back..

..