Next issue to address....

The rear fixings of the Roll Bar to the rear bulkhead only have one bolt fitted. I assume because the outer bold either side is difficult to fit with the angle of the bracing bar partly blocking the hole.

By easing off the two inner bolts I can flex the bar enough to get the outer bolts in then tighten them up?

Am I right that the plate they screw into is captive against the back of the bulk-head. ie its won't fall down if the bolts are removed completely?

Yep the plate is captive, and yes the outer bolts are a nightmare to get in easily, i'd personally run a tap through the fixing plate to make it easier to get the bolt in by hand then just nip it up with a spanner as you can hardly get a spanner on them.

Yes it was a bad design by GTM.
Would be better if plate was vertical
with bolts top and bottom.
It is possible to get bolts in but it is "fiddly".
I don't sell enough roll bars to make a redesign
worthwhile.