Problem solved. Very strange, but the reason is actually visible in the one picture I posted that shows the rubber bumper. That's where the problem was, but it wasn't the bumper itself.
Look at the picture again, and notice what the bumper is bumping against! Where there should be a smooth joint between the firewall and toe panel, mine has a 1/2 flange sticking out, for about 6 - 8 inches laterally. Both the brake AND clutch pedals were hitting that flange before they ever got close to bottoming out. The PO probably placed the rubber bumber there to prevent metal-to-metal clanging. Because the pedal was hitting the flange way down low, there way no way it could ever actuate the stoplight swith.
So, I used boltcutters, hacksaw, vise grips, and a wrecking bar to cut and/or bend the flange. When it was gone, I adjusted the brake cylinder clevis as suggested, reinstalled the switch, and everything works great!
Thanks again to all of you for getting my brain cells working again.
