Hello Anthony,
I can not remember much trouble around either bulkhead, but prior to fitting them I braced the maximum beam ( 182 cm ) with a stout piece of timber. I left it there until both seats were in.
Another difference with my configeration is that I incorperated a couple of deck beams , I have not taken any decent pics to show any of the stages unfortunately. Yet more changes made , in that I reduced the height of both bulkheads by 6mm to allow for a deck to be laid, and I cut a larger access hole in the forward bulkhead and beefed up the bulkheads to take stuff to be screwed to them.
Does not address your problem though, my instinct would be to do as you suggest and do a best fit to the bulkhead profile.
I really admire what you are doing in such a confined space !
All the best,
Steve