The 75 and the ZT used the same body in white and were built by the same robots. They were assembled on the same production line. Also the Tourer of both marques were on the same assembly line.
The 75 V8 and the ZT260 also came along the same assembly line after making a brief detour to have the V8 engine installed.
Here are a couple of pictures of the assembly line. The two workers are fitting bumpers to a Rover 75 then to a ZT saloon having completed a Tourer.
Dave T