But they're MilSpec! And manufactured in 1969. And appear to be different lengths. Maybe the frame is what really makes it a worthwhile deal? If the rubber (neoprene?) has been well cared for, maybe there ARE countless more trips left in them - because they're MilSpec.
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse