BITD, there was a Park tool you used on the period common center pull, and lower cost single pivots
and GENTLY torqued the arm where the pad was mounted, to toe in the pads .

an adjustable wrench may do ..

mafac, plain post pads the post can be flexed a bit without breaking the Swage in the holder,

it probably will un do itself back to square to the rim again, but might quell the squeak initially

chamfer the back, leading, end of the brake pad , A Bit..