Some 340 Questions

The last '66 273 4bbl stick car I had came with the 7 1/4 from the factory. I would plan for an 8 3/4 if you want to build the engine. IMO, rebuild the 340 and go with it. It will be a snappy car with the stick and some gear. If you plan to rebuild it completely, build the 416 and as Mark says, be done with it.