Interestingly, this particular turnover has never been described the way Stuart Gordon actually does it, but the way Larry Jennings and Derek Dingle have done it, which is with the third finger at the outer right corner of the card at the start, and the card held somewhat deeply in the hand. Jennings and Dingle also flexed the double as it turned over.
Gordon puts his SECOND finger on the outer right corner at the start, and holds the double at the tips of his thumb and first finger. Gordon does not flex the card as it turns over.
I worked for years on the lift, and can do it any which way (even with three cards) in all types of humidity, but it's hard as hell to reach that point.