I was working on cleaning up the bay in my 07 wrx wagon...until I hit a deer, totaling both the car and the deer. Now I'm fiddling with my Miata a bit.
The holes in the firewall are for braces, much like the ones that are already there. The tunnel is widened to clear an ls1 & t56.
With regard to shaving bays, I guess the only unique thing here is the relocation of the wiper motor.
Still have to clean this up a bit.