will it be ok if I bolt my upper anchorage to a suitable sized bracked welded to the roll bar??

cheers
matt

I don't know about the UK, but in North America you can't have the attachment welded to anything BUT the roll bar if you're going to use it at the track (otherwise if fine for road use). As I understand it, SCCA rules demand a roll-bar mount for competition....

As long as it is strong enough a plate would be fine. I'm assuming you are using diagonal and lap belts rather than harnesses. I fitted these by welding a nut to the back of a piece of 10mm plate. I then drilled a hole in the roll bar to clear the nut and welded the 10mm plate to the roll bar. The seat belt bolt then screwed into the then captive nut. You can just about see it in some of the pictures in my archive.
A point to note about diagonal and lap belts is that there is a minimum distance specified between the centreline of the seat and the upper anchorage. From memory this is 140mm (or 145mm I'll check my SVA manual)

HTH

David