In my dotage, there are inevitably occasions of problems with names that I should know well. Coincidentally, and you may say, a likely story, an old friend and sometime golfing partner from Colorado Springs is named Don Powell.
Re the grip. I always return to figure 13 of GTTB and Mindy's words associated with that figure: "The right arm turns clockwise at the start of the takeaway. This is the only movement which will keep the right elbow in position well across the body." Does this mean that fingers of trail hand must "slip" on the shaft during the takeaway in order for the trail arm to turn clockwise? Perhaps not, but I get my best forward trail elbow position, best bent-back trail wrist position, and best shot result when I allow (a slight) slippage to occur.
A question for you: Mindy believed it very important that the hips should move forward (targetward) during the takeaway and backswing. This was part of his notion of eliminating weight shift in the backswing. Does your version of Blake include forward shifting of the hips during takeaway/backswing?