Hi BigJim,
Thanks for that. You were spot on.
Finally got the rear plate on. Problem turned out to be following Haynes and leaving the mounting bolts 'loose'. The plate wouldn't span the gearbox mounts until the bolts were pulled up.
Never realized the front plates were engine mounts! It's what happens when you get a bike as a bucket of bits and you've never seen one before. The frame and front plates are powder coated and yes, all the clearance has been lost for a sensible fit. Time for the angle grinder!
Best Regards