I have a result! The good people at Historic Helicopters have sorted me out with photos of the missing pieces to complete the jigsaw and have also offered some of their spares stock should we go choose!
Complete H.1400 engine and coupling assembly ready for installation into aircraft:
Drive shaft, with Thomas coupling, as it fits to PT output shaft:
Torque tube (actual term Support Tube!) with yoke to connect to the gearbox gimbal ring:
Thanks to everyone who has helped in my search, it is much appreciated
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