Solution (for now)
Thanks to a fellow builder in the UK (Mike at EGHO) who sent me a photo of his nearly completed bird, I now know which holes to leave open. For anyone having the same question as me they are as follows:
Counting forwards along the longeron from the inspection panel opening, so that the hole corresponding to the aft piece of the F-711 bulkhead is labelled "1", the holes to leave open are 5, 11, 16, 20, and 23.
Hope this helps someone in the future.
Andy @ EGLM/EGTB
RV-6 (Shared, Bought Flying)
Building RV-7 #74424