[lust4speed]

Just for clarification, Gates 7xxx series is listed as .410" wide and Gates 9xxx series is listed as .500" wide. The 9xxx series is the width called for by Pontiac, and the 7xxx series is pretty close to Pontiac wanting a 3/8" belt.

I had to use a 7xxx series with the Vintage Air Sanden compressor because of the narrow groove in the compressor. A wider belt would have rode way out of the groove. Luckily, the stock Pontiac 3rd pulley on the other end was deep enough that the belt worked good. Originally on my '67, Pontiac called for a 1/2" wide (9xxx) series belt for the compressor and the power steering unit, and a narrower belt for the alternator. Using the 7xxx and 9xxx on the water pump pulley has both belts riding exactly the same depth in the grooves.