Ok any doubts I had about my sanity have been relieved after last night, it just does not fit !!! i unbolted, removed, inspected, cleaned, replaced, wriggled, shuffled, picked it up and dropped it, hung off it, etc etc, it just will not sit any lower.
The mounting point inside front is sat flush on the windscreen surround in as much as you could not get a feeler gauge in there but still the side needs to be about 20mm lower
My conclusion is that there must be a different version of the roof that either the sides drop down 20mm further or the mounting point "box" at the front of the roof would be 20 thinner.
I have not unbolted the screen and moved it out of the way yet but it is obvious that if i did the roof would then sit properly on the side panels.
I ran a straight edge along the roof side and along the tops on the side panels and all is as straight as can be expected.
None of the other body panels have been moved or unbolted and the original roof i removed was not under any tension when i took it off.
Ill try to post some more photos from my mobile
As mentioned in previous replies, i have taken a couple of measurements, placed a flat edge across the windscreen resting on the underside of the gutter each side then measured from there to the underside of the front roof lip and it was 65mm
And from the underside of the lip where the screen folds to the underside of the roof and it was 19"
Again, sorry for the mix of metric and imperial