I found this:
OK - I've just passed through RAF Cranwell myself and here's the essential numbers you need:
Pilot:
Weight: 56.8 - 94.0 Kg
Functional reach (shoulders to thumb-tip):
740 - 900 mm
Sitting height: 865 - 1010 mm
Buttock knee: 560 - 660 mm
Buttock - heel: 1000 - 1200mm
Navigator:
Weight: 56.8 -94.0 kg
Functional reach: 715- 900 (note shorter)
Sitting height: 850 -1020 mm (safe to be alittle bigger)
Buttock-knee: 550 - 660 mm (little shorter)
Buttock - heel: 970 - 1200
This looks like 8 st 14 lbs.