These are for sale for $270... a joke, but that is how much they owe me in time spent anyway. They were supposed to be 400mm ATC and they're 395mm. They can fit a 3/8" axle/1.3" diameter peg or a 14mm/1.5" diameter peg. The 14mm (axle thru hole) peg fits pretty flush with the cutout so its probably the better choice.
This is the reason a few BMX companies have turned to cast dropouts with this peg cutout: they only require plugging the dropout into the leg and brazing into place.