All Rover springs are 6" diameter at the center of the coil except 110/130 rears which are 7". Ride height and free length depend on the application. http://rovers.red90.ca/springinfo.html
There should be no stock ride height difference between any 90s, NAS or otherwise....
Now to get more specific... I have used both Airlift and Firestone bags. I found them both a bit short for a stock 90 rear height and needed a spacer. If lifted, you will need more spacer. Airlift bag's are longer but the kit does not include a bottom spacer while the Firestone bags are shorter and have a bigger upper spacer and a lower one.
I keep meaning to ask both companies if they have a longer bag that would better suit lifted vehicles.