Be careful of the Blue Book if it's a stage car - modifying the bulkhead may not be an option -
"48.1.4 With the exception of cars accepted under 46.3 (see 46.3.7), and cars with modifications conforming to their homologation papers (46.2) floor pans, bulkheads and transmission tunnels may not be modified other than by localised alteration to accommodate the fitting of an alternative engine and/or gearbox and/or differential and/or axle, seats and exhaust."
I'm not sure if the MSA consider it a bulkhead though.