ellingtj,
I fear you may be correct and ZR is different to
BRM. Haynes 3399 page 11.9 bottom right picture 13.3b shows 200 door handle tweater, which is same as
BRM. I've had a look at MG Driven to Extremes page 18 and ZR is quite different. You're just going to have to hook the door panel off and take a look.
As you say Haynes page 12.19 shows the base mid (Rover 4 watt max, wow !) the picture does not really show how the three screw plastic mount steps the speaker out about an inch. I think there is a very high chance the ZR will be the same. I think the tweater might be the same too just mounted differently.
I fitted Sony XS-HA 1724 (150W

) these have a silver metalic cone in the centre of the mid range which is visable through the silver metalic mesh
BRM grille - tasty
For the ultimate rear it has to be a stealth shelf from Acoustic Solutions, the best £90 you can spend. Check their website, see the thread on bass box.
Hope that helps.