There are quite some small differences between ZT 260's and Rover 75 V8's, in that ZT 260 shock absorbers and springs are stiffer, fore and aft. The ZT 260 has a rear anti-roll bar, which the Rover does not. ZT 260's have small dampers on the diff, absent on the Rover.
Saloon and Tourer spring are (theoretically) different, both for the R75V8 and ZT 260, but availability of the correct Tourer springs can be problematic.
In the case of 260's, there was a change of design of the rear springs. Not related to the Mk1/Mk2 change point. To that extent, later model springs should be sourced if possible at replacement. More details here: https://www.two-sixties.co.uk/mgoc26...hock-Absorbers
I know of no other no other changes in suspension, spring or damper rates etc. over the whole production period.
The Steering rack and steering rates, are the same for all models, all ages.