Note that construction technology did change (and evolve) thru the boom years of the mid to late 70's. While the FRP overhead "pans" conferred several production benefits, it also had some limits. Our previous Niagara 26 had this interior pan, and some movement around the main bulkhead was just considered acceptable.
In most (all?) of these designs, the slot where major bulkheads was fitted in did contribute to overall strength. Even tho in later years the builders would keep upgrading to an adhesive that helped to 'lock' the bulkhead in place, there were limitations to how much strength they could guarantee.
By the later years of the long model run for the E-35-2, EY changed over to a stick-built interior, even going to teak in the '78 and '79 builds. I really do not know when this change started, so perhaps a former employee can chime in. They may have changed the layup schedule for part of the deck, as well.
Given that by the 80's, EY was tabbing in bulkheads and other furniture, they knew the value of making the whole boat a monocoque structure. A lot of other high-end builders were doing this as well. Our Olson was built this way, I should note.
If removing a part of the original liner, one would want to do at least some structure analysis on a napkin, just to be sure of enough residual rigidity. That's only IMHO, of course.