Change 1-2 gears to lower ration gears 1967 Dart Automatic (904?)

I just do the math.
As always; talk to the TC supplier. They have access to better information than I do.
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I really liked my 2800, but I think a 2600might have been enough.I just wanted to spin 275s, and eventually 295s, and that was what the 2800 was for. I already had the 2.74 low, and 3.55s, so my starter gear was 3.55x2.74=9.73, which is equivalent to 3.97s with an A904 low gear of 2.45; and my hiway rpm was 2870@zero-slip, so I went for the bad-boy 2800. No regrets.
I actually bought that TC in about 1980 for a slanty powered 69 Barracuda. Boy-O-Boy that slanty jumped off the line pretty good. When I sold that car,I kept the TC. Then in 2000 I had a new application, my winter motor.
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I can say tho, that with 3.93s already, your starter gear with an A904 is 3.93x2.45=9.65. so all you need to break loose say 255s is about 1400ftlbs, so
1400/9.65=155 ftlbs out of the 318. at 2400 that is71hp. at 2800, that is83hp
So I think either one will get the job done, using less than full throttle. Once the tires are broke loose, you can just run the rpm up to whatever you want, and let the tires catch up to the road.
So for showing off, the 2800 is great. but spinning ain't winning, lol. so you might have to ease it out at part throttle. That's typical with a street chassis.
The 2400 might let you use more throttle with a little less wheelspin.
The 2800 also lets the secondaries open on a vacuum secondary carb, and that kicks in some additional power earlier. And That is what I liked; massive wheelspin,lol. Ok not massive,exactly. What I really liked was the Thermoquad moan, accompanied by the BFG howling.

I assume you have an LSD? If not, you're gonna need one one first, else you'll just be peg-legging all the time, and that makes kicking the back out around turns....impossible; and that takes all the fun out of it.