Any pictures of the two side by side for comparison?
I would just keep my eyes out at a rally and check each out. Finding 2 rovers with the diff cards and parking next one another for this purpose probably has not been done yet. Ill keep my eye out. If I see any series rovers around Ill stop and check, cause you know we all do that anyways...
easy way to tell is the anti-burst latches have a rotating latch on the door and round stud striker on the b pillar like a modern car. the non a-b have a simple in/out latch almost like a cabinet...
here is an anti-burst latch from the web:
didn't see any good pics of the business end of a non a-b latch in my quick search...
'72 Series III 88 "Greenie"
'85 90 2.5NA "Stinky"
My '76 SIII has the cabinet style sliding latches, not the anti-bursts, but it's a RHD from England (so it's ROW not NAS). I wonder when (or where) the anti-burst became standard?
'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S