Exactly, With the stock GMC rebuild bearings, with sealed bearings they dont let the oil circulate through, so they therefor build up heat and fail at higher automotive speeds. What you want are the double ball race ball bearingsfor the front, and the single ball race none sealed for the rear packed in grease for lubrication

The plenum has to be the same size as the blower discharge port and as high as the intake port cross section height.