I never used them, either; did used to make our own from heat riser valves way back in the stone ages, though. Stacy David put a set of cutouts on his Rat Roaster '32 roadster project a couple of years ago; I don't know if they were Doug's, but the were electrically operated. He put them at the end of the collectors on his headers; had to notch the frame to get the actuator motor up horizontal, put a nice turndown on the end after the cutout, and tapped the header collector ahead of the valve and ran the muffled exhaust under the car. Looked to be a good project. Check out his site at "Gearz"; google or search "Gearz TV" or Stacy David, and go digging around for "Rat Roaster".