Hi all, thanks for all your inputs, one way or another I have been steered in the right direction.
Just for the purpose of updating the situation, A visit to the recent "Newbury Autojumble" with my tape measure confirmed two things, there is no real difference in the roof dimensions, across the early defender range at least and, the side gap viewed on the side of the roof where it sits on the windscreen surround varies from nothing up to about 20mm.
Now I know the roof is the right one I set about checking everything else in more detail and, with the aid of my brother in law, concluded that my years of off roading abuse must have beaten everything down and distorted the original roof so, I loosened the bolts which hold the tub to the outrigger, loosened the sliding bracket the holds the sides to the tub, jacked the side up with the farm jack and used ratchet straps and clamps to get all the roof bolts in and tightened up, 70% of the bolts fought me every step of the way but, in the end I only had to use the drill once to slightly enlarge one hole.
So, the roof is now bolted in place, the only sacrifice is that I have a gap between the sides and the tub although this is only about 5mm tapering to nothing at the rear, it may settle after driving around for a bit but I need an MOT first and I've bought a tube of black mastic just in case of persistent drafts.
I guess after all, what seemed like an massive gap at first turns out to be a few mm here and a few mm there which add up to more than the components.
Thank again for your efforts and I will leave you all now to concentrate on more worthy issues.
