BLACK OUTpower brake conversion for the 1967-72 Chevy and GMC trucks consists of a 9″ black vacuum booster, POL or Wilwood master cylinder and Black Outadjustable proportioningvalve. Performance Online introduced this item in 2013 and received a huge response. This kit adds a nice professional detailed look to your classic truck. Improves stopping distances and driver performance tremendously.A must when converting to an LS engine where additional space is required.