The '71 would just have been the simple H-block design, prior to the proportioning style valve in Steve's picture. But it still uses the same style switch it looks like. Aftermarket ones now have a single post switch, rather than the dual post of the factory.
Screwing something into the switch hole to help re-center the piston might make sense, but I would hate to see metal shavings get even into that isolated little pocket in the piston's notched area.
They sell tools for doing that, but I think they are made of plastic too, and are more for holding the piston in the center while you go about your business bleeding the brakes and such. Not sure it could handle being used to re-center a recalcitrant piston.
It's more work, but you can remove the block from the frame, remove the end cap and remove the piston from the block. Clean it up and re-install in it's centered position to be held in place by some tool or another.
Then when things are all buttoned up and working, reinstall the switch and wiring.
And then pray!
Paul