Float sticking open could definately cause the flooding. This was a semi common issue on the old 2-jets. They would flood so much, raw gas could be seen seeping out from the base gasket on the intake manifold. The trick of the trade was to rap the side or top of the carb body (where the float is located) with a small hammer.
Sounds like your carb might have a piece of dirt or debri stuck in the seat, if you weren't thorough cleaning after disassembly...
If you order a back-up carb, make sure it is for a 1980 or older. 1981 and up would be computerized. I think the Dual Jets for the 301 2 bbl (Y Code) are basically the same. 231 V-6 after 1977 might also be the same, but I would cross reference them on NAPA or Advance Auto website to be sure.
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