71 Dart A/C car heater issues
OK so here's pictures. What appear to be studs hanging down from the dash are actually simple bolts inserted down through holes that I believe are on all the dash frames. They are retained by a nut tightened against the dash frame. If you don't have holes already let me know and I will get you measurements.
You put the ducts on from the bottom, there is a nut with a captured washer that goes in from the holes on the bottom of the duct set through metal pieces between the ducts. I think that the only reason the "studs" are so long is that it makes it easy to thread this second nut with the ducts in place. You need a deep 7/16th socket to tighten the duct retainer nuts.
OK so here's pictures. What appear to be studs hanging down from the dash are actually simple bolts inserted down through holes that I believe are on all the dash frames. They are retained by a nut tightened against the dash frame. If you don't have holes already let me know and I will get you measurements.