Upgrading to a multiple Carburetor set up will be much more efficient if you also upgrade to a better flowing exhaust system. There are a few paths that you can take. One is to have headers made, second option is to buy a set of cast headers from Langdon's Stovebolt, the third would be to contact Tim Kingsbury and/or George Ashe to have a stock manifold split into dual exhaust.
Think of it as a air pump, the more air you bring in, will require more air to get out, in layman's terms..... And more air flow equals more efficiency, which will yield more horsepower.
Just upgrading the exhaust alone makes a huge improvement.... I visited Reg Evans on Monday, he installed dual exhaust on his Dodge with a 230 in it, and claimed that the dual exhaust made it seem like his engine became a V-8 from the improvement in performance. I thought that it also looked nice. But you may need to make some fuel pump modifications depending on what arrangement you currently have.
But you must figure out how to get your transmission to work out. Or go the easy path and convert over to a manual transmission.
This is my opinion offering, I have personally modified six cylinders in other configurations and makes and always have had amazing results. All sixes benefit from improved induction and exhaust flow.
Good luck, I hope that you get the transmission to cooperate with you.