Manual transmission conversion into 72 Duster

I have built a couple of those S-10 transmissions, and I can tell you that;
IMO
any 318 or bigger SBM, running a decent tire and a SureGrip will kill it, and it won't take long. Forget this idea.

On the flipside; the Regular A833 is one tough item. Build your engine right and a 4-speed is all you need. Build it like an old 302 Rustang and it will last forever.
If you want to run the A833od, your engine will need to have a short,wide, powerband, on account of that od box is a 3+1 trans. The ratios are; 3.09-1.67-1.00-.73od, and the splits are
.54-.60-.73
Which looks good on paper. But in real life and by my experience with a 367HO, pretty much sucked for me. Your results may vary. There is a reason you can buy them so cheap.

But as to fitment of the A833od; yes the longtail will fit no problem ( I have one in my 68 Barracuda.
Well except for;
1) a lil grinding of the front shifter-mount, which wants to occupy the same space that the T-bar X-member does, no biggie just grind it to fit.
2) you will need to fabricate a new adapter on which to mount the shifter, and
3) fabricate new, longer, stronger, shiftrods. If you position your adapter right, you can make these a straight shot, and
4) you will need to fabricate a new custom floor hump to accommodate the non-stock shifter placement and the custom rods. which leads to
5) the carpet will no longer fit, so out comes the knife.

But beware the 3-4 shift!
that 18tooth overdrive gear will not take any abuse; and when it blows up, and it will if you forget that you are shifting a 3+1, then it is well able to take the rest of the trans with it. Not every time mind you; out of the Three I blew up, one survived and took me home. So
keep a spare handy.
For performance;
If a stock Low-compression 318 is used, she will really like that 3.09 low gear. But when you shift into Second with that Smoggerteen, it's all over. Unless you have installed say at least 3.91s in the back.
If a stock low-compression 360 is used, then 3.73s can be used
If you pump the CCP (CrankCase Pressure) up on either of these, to close to the max for the fuel you intend to use, then they will put up with 10 to 20 percent less gear. But I mean; "put up with".
The goal is to have a decent usable Second gear, the gear you are gonna be in, for most of the time. I like an overall ratio of 6.80 or a tad more, with my 360HO. This gets me 11.7 mph per 1000rpm, so 3000=35mph/ 6000=70mph. There you go.
To do that with the 1.67 Second gear, will require 6.80/1.67=4.10s.
But that makes the starter gear to be 4.10 x3.09=12.67 which is super-low, and makes dropping into Second a very early shift. Or if you are in a hurry, you will have to really rev it out, to cover that .54 split. To drop into Second at 3000, will take 3000/.54=5555 rpm in First; see what I mean? If your engine is a low-compression big-cam slug, 3000rpm is way off the cam.
I ran this 3+1 behind a Smoggerteen, with a 4bbl, headers, and 3.55s; for just one winter. That was enough for me . I ran it for a couple of years behind my 367HO, trying all sorts of rear gears, and that is how I came up with the 6.80 overall Second gear. But in the end, I just couldn't stand that 1-2 split of .54.

The Regular A833 has ratios of 2.66-1.91-1.39-1.00 so the 1-2 split is 1.91/2.66=.718. So now reving First to 5555 will get you
5555 x .718=3990rpm, close to peak torque in a stock 340. And to drop into Second at 3000 will take 3000/.718=4180 in First. This works really really well with any SBM. Of course, the more CCP it builds, the better it works.
To get the 6.80 Second gear with this Regular trans, takes;
6.80/1.91=3.55s hmmmm, no wonder 3.55s are the street gear of choice with this box.
To pull that 6.80 gear at 3000 or less rpm(35mph), will take a stout engine. Which I have. Which a stock 318 is not. And a stock 360 sorta barely is. But don't try to rev either of these stockers to 6000!
lol.

IMO
for a fun combo;
any 318 with the Regular A833 and 4.10s is REALLY-BIG fun ..... around town. Been there done that; but 65mph is about 3350, so there's that.