A903 3 speed to a833 od

The simplest solution is to change the yoke on the driveshaft, to match the trans.
AFAIK there never was a small shaft short A833 direct fourth trans made.
But there were with the overdrives.
I suppose the overdrive M/S could be adapted to work with the regular A833 by fabricating a third-gear bushing; but the 3-4 synchronizer would also have to be used. Not sure if those parts will play nice together, I've never looked.
But it's a bit of a pita to swap mainshafts.
Much easier to just swap yokes. 10 minutes with a big hammer and yur done.
OOps I missed that you ordered an A833od

In this case , the ratios are very similar to the A903, but with the addition of the .73 overdrive.
I'm guessing you are also contemplating a rear gear swap. For the 170, that sounds good; cuz not sure she could pull 2.76s at 65=1800rpm IDK. Meh, that's only ~130 ftlbs required so maybe.