Denvers came in 81AS, 19AS, and 99AS...I have the CC spec around somewhere. The smallest chambered ones, the 81's, were 60CC.
They were listed for natural gas or high altitude use. I am pretty sure the S means something like special and is for a replacement part that was not used in actual production...
I think they were only briefly available and were discontinued before stock car racers discovered them, hence they were always rare and desirable. They weren't even cheaters, really...I think most of the stock car racer rules specified real Ford iron heads...voila!
By mid-1950's the allowable better head was the Canadian C7RA, aluminum and only slightly smaller capacity than regular 59, and these were soon joined by fake C7RA's made by Weiand with considerably smaller chambers. The Weiand ones were more or less standard equipment in the last days of flathead stock car racing.