Thanks for the replies.
I have no idea about this subject matter, but it was the radio relay FV439 vehicle with the masts etc stowed on the roof, that I was going to model.
Ptarmigan Triffid/Radio Relay FV439 - Military Scale Models - HMVF - Historic Military Vehicles Forum
I understood, possibly wrongly, that the Wavell system was fitted to a separate vehicle designated FV435, with a large box structure to the rear of the hull, so started a separate thread for that.
I was looking to do both, but I know next to nothing about either.
Thanks again, Ian