Thanks for all your help folks! It seems to be between 7.5 R16s and 235/85 R16s. Now just to work out costs. The Deestones look class but I think they are only crossply?
Gooing to put the original wheels back on and a sensible set of tyres. Maybe repaint it the proper Limestone colour it used to be. Also wouldn't mind a new rear-crank oil seal to be honest!!!