Al-
Your best bet is to find an original carb, and if you can't rebuild it yourself have Mark A or Jim C rebuild it for you. Even if you can't find the original big window carb, the one barrel Aisin with the little sight glass, w or w/o the solenoid up to '67 is still the best choice. One barrels show up occasionally in the classifieds here or Ebay. If you find an Aisin that has a solenoid just run a wire to the positive side of the distributor.
Otherwise any of the early Carter, Rochester one barrel carbs for a six cylinder would be close enough and get you in the ball park to keep running.