India Four Two, iirc, there was to be a series of King's Cup Air Races and Schneider Trophy Air Races and the Flying Selection Squadron were chosen to represent the RAF using the Chipmunk. Some of the RAF's fleet were VHF equipped, some were UHF using PTR 170. That was a 12 channel set, crystal controlled. This was incompatible with airways transits and the civilian airfields that the crew had to establish contact with as they were all VHF only.
The Becker was presented to me by the fleet Engineering Manager based at RAF Swanton Morley for installation on one aircraft. I don't recall if there was a requirement for it to be easily removed and installed in another aircraft in the case of an unserviceability. Nevertheless, I had my ideas where it was best installed and the Squadron management had theirs! I preferred the removal of one of the instruments which wasn't on the Minimum Operating Requirement list and fitting the radio to the panel. That's why it ended up being in a really awkward place to be operated. '331 (A) was chosen by Squadron engineering management in consultation with the Aircrew. A different propeller was fitted especially for the races too, but I don't recall the details - coarser pitch I think.
As for when, I can only quote Dan here as it being 1985 which ties in with my ever diminishing memories. I removed the Special Trial Fit and left the Squadron not long after the races finished. After that there was a mod. programme and the aircraft got all tarted up with the new radio and a heater!