TT, true, the K1, like the Vulcan 1s had the Mk17 regulators which could only deliver 30mm Oxygen overpressure to 50k and no pressure suits. The Mk 2s originally had the Mk21 which could deliver 70mm at 56k.
Even on the Vulcan I only went over 50k 4 times and 555 on an air test once.