John, Bob, et al,
Here's the scoop on the footrest fastenings.
The upper, forward end has two slots for bolts. The slots' outer ends
are 7/8" inch from the edge of the folded-up extension that fits against
the firewall. The slots themselves are 1/4" high and 3/8 inch wide---that
is, the things could be drilled with a 1/4 inch bit, then enlarged to be
the 3/8" wide.
The bolts for these slots are 3/16 WW. The outboard bolt passes
through the footrest and the firewall, and its nut is in a hole that is
straddled by the bracket for the downward-sloping firewall brace. It's
also a 3/16 WW nut, that it not immediately visible at first glance. The
inboard bolt is same size, and its nut is just inboard of that same
bracket, as the bolts are roughly 2 1/2 inches on center.
Ed observed that one needs about 3 ft of extensions. That's right, if
you want to have full swing on the ratchet wrench, in the clear behind
the dashboard. If you use only 2 ft of extensions, you may be able to
reach the nuts on the engine side with your prehensile right arm and hold
a wrench on them.
There is a good cubic foot or more of empty space under there, BTW.
Perhaps someone can come up with an idea for a hinge and latch arrangment
that would allow this footrest to flip up and make this useable storage
space. Would certainly hold a plastic peanut-butter jar of distributor
cap, rotor, condenser, etc and a fuel pump (all the parts we carry for
our MGA and MGB friends, not for ourselves, of course).