how far back does the big block in your a-body sit?

just measured 2 things:

there is an indented part of the firewall (looks about where the heater sits against). From the rear center valley pan bolt, it is 3 1/2 inches to the sunken-in part of the firwall.

Also, from the firewall surface where the master cylinder is, it is 23 1/2-24 inches to the water pump mounting surface (if you drew an imaginary line out toward the fender)

It does not appear that i'd be able to get anything on the top tranny bolts to remove them if i ever had to.

hope this is clear enought for some of you big-blockers to measure what you have