Originally Posted by ccjames
how do I remove the four screws that are entirely rusted that hold the bumper on the rear frame?
On our '74 the upper screws were (still) the countersunk type, the lowers were hex head... so the lowers came out relatively easily after a shot of penetrating oil. The upper countersunk slot-head screws were stuck tight. On one side I was able to use a handheld impact driver
(with a wrench on the nut), and on the other I had not much choice except to drill it out. I started with a 1/8 inch bit (you should already have lots of those for popping rivets), drilled in about 1/4 inch, and then switched to a 5/16 inch bit to basically pop the remains of the head off the shank of the bolt. When doing this it's a good idea to grip the nut side with vise grips.
The next level solution would have been "angle grinder". But, that would have been tricky from the inside, given the proximity of the frame channel.