The firewall setback is only 2 1/2" and is a function of the distributor clearance.
Miles to go but I'm good with this so far.
The rear floor is rosette and seam welded in place and fit better than I had hoped. No problems with the installation.
Four crossmembers and the front and rear originals make this a strong installation.
I purchased replacement fenderwell panels but am unimpressed with them. The panels are 22 ga. and are not as strong as the original A units. I feel that the fenderwells are an integral portion of the rear quarters and these cannot replace them well.
Haven't decided which way to go yet.