[Ronald G. Stephenson]

The understructure on the Bristol roofs is likely to be small diameter tubing, as is the practice on aluminium bodies, but they may have fabricated a flatter 'slat' sort of thing in an effort to make more headroom, but it is a simple matter to re-inforce what you have with additional material to surround the new opening. Trust to the people who you select to do the work, and ask questions as to how the do it, and by all means, look at some of their work before you commit. Good luck.