DCNF Carbs 4 bolt vs 5 bolt

I'm in the process of rebuilding my 79 308 DCNF Carbs 72,73,74,75. I ordered kits from Weber Carbs Direct and asked for 5 bolt kits. They sent 4 bolt. When I contacted them to get the gaskets replaced they said that it would be difficult to get 5 bolt gaskets. Does anyone know why Weber produced the two kinds of carbs, when did they change and why? Are the 5 bolt the older ones and is that why they are harder to find? FYI I asked about the status of the Weber Co. and they told me that Weber did not close down but was on strike. They also said that the strike was over last week.