Transmission/Torque converter ideas

I have a 408 in my 73 duster and currently have the 727 tranny..with 3.23 gears......I have run the 904 with the lower first gear and it is way faster....I plan to go back to it. As for the the 850 carb...I would not go above a 750 unless you have a really high stall and lower gears.