A833 Tail shaft
Maybe I said that wrong;
They are low rpm transmissions cuz on the 1-2 shift, the Rs fall to 54%. So then, shifting at;
4000, the Rs fall to 2160, for a powerband requirement of 1840
5000, the Rs fall to 2700, for a powerband requirement of 2300
6000, the Rs fall to 3240, for a powerband requirement of 2760
7000, the Rs fall to 3780, for a powerband requirement of 3220
There is no factory SBM, normally-aspirated, with a powerband of 3220. At BEST, you can expect 2000 rpm, and more often than not, closer to 1500.
Therefore, the A833od is, a low-rpm trans.
As you know, the 340, even the hi-compression version, never had a bottom end to brag about, so if you install a 7000 rpm cam into it, without a corresponding increase in compression ratio, the cylinder pressure will go away, and with it goes the bottom end. Asking that big cam engine to pull from 3780 to 7000 is to drag the average power right into the basement.
Whereas,
if you put a low-rpm cam into it, the cylinder pressure will go up; and now you have more low rpm power, and so the powerband requirement becomes more bearable.
However, the biggest problem with that trans is not just the 1-2 shift, but trying to put Second gear where you need it to be, without getting into Third/Direct too soon.
Most of the life of a streeter is spent in Second gear, so I want that gear to work for me.
After 5 decades of driving A833s;
I like my second gear to run from 30/35 mph to 55/60mph. With 27" tires,
From 35 to 55 is 63.6% so my powerband has to fit into that range.
and I like to be wound up tight by 65
This will take a Roadgear of 8.00.. With the
8.00Roadgear; 30 will be 2990, and 60 will be 5980, and 65 is 6480
Now, how do you get 8.00Roadgear with this A833od?
To get it in Second gear is 8.00/1.67=-------4.79 rear gear
to get it in First gear is 8.00/3.09=--------------2.59 rear gear.
IMO, this is a nearly insurmountable problem.
Your Mopar Second gear choices are 1.92, 1.77, and 1.67; there are no others. So then;
8.00/1.92=4.17 rear, and 8.00/1.77=4.52rear
OP has 3.91s; so 8.00/3.91=2.05; the closest Second gear is the 1.92.
With OP's 3.91s, 27s, and the A833od; 30mph =2440 in Second gear, and 60=4880, soooo this is a low-rpm engine. If your 340 is typical for stock, it will power-peak at about 5000.
I think Second gear will be a pretty good match.
And that is why I said;
in your case; and if you already had it or could get one cheap, I would try it.
As you can see I am not, repeat, NOT, arguing against the A833od in this case.
Now lets talk about the other gears.
The starter gear is 3.91 x 3.09=12.08.. This is 10 to 20/25 percent more than the 340 Duster needs on the street.
The cruiser gear is 3.91 x .73=2.85 and 65=2310/perfect
Direct is 3.91 x 1.00=3.91, and 55=2700, so a 340 might have to shift into Second to pass a slowpoke, and then; 55 in Second=4470/ perfect , SOooo, all-in-all, not that bad a match.
In this case, with the 3.91s, the biggest handicap is the 1-2 shift.
My experience:
To me, with 3.55s, revving it out to 4000/29mph in First, to get into Second at 2160/29mph, was just too much like a Mustang, I really despised that. I had a hi-pressure 360, which actually pulled pretty hard from 2160, but
not
hard
enough.
After two or three summers of suffering, I swapped that trans out.
Besides that, I kept breaking them. Two of them shattered the tiny overdrive gear. In a third one My 367 ripped all the input teeth off.
I was done with it.
OP;
Whatever you decide
Happy HotRodding.