bocephus You should be able to get the gauges checked at the county extension office, or they will know where to go. I use Presto canners, and have converted all of mine to weight types, much easier. The weighted jiggler keeps the pressure steady without me fooling with changing the burner to keep the gauge set.
If the old canners are All Americans, they don’t even have a seal, just make sure the mating surfaces of the pot and lid aren’t chewed up.