If I still worked at Crewe Toll, I could tell you - there used to be one on a stand in one of our staircase landings (there was a Blue Parrot on our floor, IIRC).
24 inches is at the upper end of "about right", but that's a decade-old memory. The best result for "AI.23 radar" on google images is from a spanish-language website, and to my dim memory it looks more like TFR (the TSR.2 set) than AI.23. IIRC the AI.23 was shaped to fit the intake and was more conical towards the rear, not cylindrical.
As ever, I apologise for my inaccuracies...
Edited to add,
"found a link".
