''But RAF Chipmunks DID eventually have heaters! Mod H335 introduced in 1979 involved fitting the Canadian style heater system, detected by the small projecting intake in the front of the cowl and the steeply raked exhaust stack - it's readily apparent in the photos of the EFTS formation for instance.''
Yes, and it did an excellent job of raisng the temperature of your left leg by two degrees!
''Does anyone know about the background of the UHF conversion. It must have been incredibly expensive. Were these sets designed and built for the Chipmunk or were they used in other aircraft?''
RAF Chippies has several radio fits. I have flown them with four fits. First, the crystal VHF sets which had only about 8 channels numbered from A to G (?) with a controller on the coming (as fitted to Spitfires in WW2). Later these were fitted with a tuneable Marconi radio which had 720 channels, controller again on the coaming. The original PTR170 UHF set had again a limited number of channels, 1 to 12. Contoller yet again on the coaming. Later, some were modified with the PTR1751 with digital controllers in each cockpit which were the same ones as fitted to many frontline arircraft and even had the ability to control frequency agile anti-jam Have Quick 2 radio tranceivers - a bit excessive in the Chippy!
The EFTS aircraft I flew had the PTR1751 UHF sets with a separate Dittel 720channel VHF which was under the intrument panel by your right knee in the front cockpit and very difficult to see and tune.
Army and Navy aircraft had different fits.