I completely understand wanting to duplicate Ludwig's non-slip pad for authenticity. BUT... using that material in today's real-world playing just doesn't make sense to me. It would wear very fast! I would think that just some kind of non-skid material would work better. Again, if you really want to go for authentic, then I'd certainly go with the closed-cell foam.
You do have an excellent point and I considered making improvments via todays advancement in drum materials and design. There is a guy that sells refurbed Speed Kings on Ebay that re-engineers the flaws of the Speed King and sells them for a whopping $149 and I have seen purists on different forums ripping him a new one for changing the pedal from it's original design. That was the impetus for me to try to just stick to the original Ludwig design. I think he does outstanding work on his pedals and am sure they are probably well worth his asking price since he powdercoats them and fixes all the squeaks. Many of the drummers that are in the market for a refurbed Speed King usually know how to care for them and play them to get the most out of them.
In my mind, Velcro would have been the first choice since it provides great gripping abilities on drum rugs and some manufacturers put it on the bottom of their pedals nowdays but again, I wanted to go the route of staying true to Ludwig's design asthetic. The only Speed Kings I "re-engineer are the ones that come in with all the slop in the heel plate due to the hingepin gnawing the holes of out round from all the side to side movement. On those, I grind off the hingepin, install 4 small acetal based perma-lube washers to eliminate side to side movement and stop the metal to metal contact. If I get a pedal in that's tight with no slop, I leave it alone and just lube the hingepin.
Thanks for verifying the measurement of the pad, MLayton. You rock, bro. Thanks for your invaluable help.