Help to ID very Strange 426 Wedge Block

Something I'd read from way back when... During the early days of restrictor plates on super speedways in the early seventies (sometime after the introduction of the Boss 429) it's said that some plate designs worked better with wedge heads, others worked better with Hemi heads. I'm guessing we're looking at a hens teeth early seventies NASCAR wedge block, with the ability of being set up for cross bolt caps. What's stamped on the ID pan at the front of the valley?