Wondering if anyone knows a source of the vent balls/louver thingy that goes inside the dash's side vents? Right now I've just got the round trim piece, but no ball inside of it. I'm not really sure what to call them and haven't found anything online for our 75-78 trucks. I did find some for the 79-83 trucks on eBay, but the housing is square not round - anyone know if the ball inside is the same diameter? BTW, who can explain the heater/vent system in our trucks w/o AC? Do these vents just bring in fresh air from the cowl, without heat integrated into them? If so, do the "balls/louvers" have a way to close off the cold air in winter? On my truck it seems the heat only goes through the dash/windshield defroster slots or through the box under the dash, not through the vents.