The test were indeed on a rocket sled, and I think the high wind blast test was done with a fighter helmet on and it stayed attached. I suspect that a 'bare face' test would have probably done irreparable damage to his eyelids and mouth.
You may be getting confused with the g forces that he experienced which severely distorted his face and nearly blinded him, and I'm sureI have seen lots of pics of those around.
I seem to recall that there was another series of sled test which went above the 40 or so 'g' of Stapp towards 90 - and he survived too? I think the record ejection was Mach7 from an X-15 but obviously at a low IAS.