This is not an altitude record per se but did involve a piston powered helicopter.
Later the same day as Bading's evacuation to definitive medical care, May 20th, Link Luckett flew his Hiller helicopter, stripped of everything including the starter-battery, to 5200 meters (17060 feet) and extracted John Day. The next day he repeated this amazing feat to similarly rescue Pete Schoening at the same altitude.
I have seen a photo of Link taking off his boots prior to takeoff....to save even that few pounds of weight.
