A833 OD or 727 behind a 440. Suggestions and questions

Tire size, man? 3.91 could be fine with tall tires, say 30s.
A 30" tire with 3.91s, would act the same as 3.13s with a 24, or 3.55s with 27.2s, or 3.23s with 24.8s.
So don't panic yet.
While 3.91s are more than the BB wants no matter the realistic tire size, 3.23s could easily be made to work with
IMO, a good starter gear for the big 440 might be about 8/1, corrected to a 24" tire. And that would math out to the 2.94s and 27s;
3.09x2.94 x 12/13.5=8.08, so that is enough first gear. But second is quite far away, and probably will not like that 2.94.
For second I like a 6.06 ratio, corrected to a 24 inch tire.
With those same 27s as above, this would ask for a rear gear of 4.10s
1.67x4.10x12/13.5=6.08, so that is what second wants to have similar performance to a regular 4 speed in second, with 3.55s
1.92 x 3.55x12/13.5=6.06

Now since you already have the 3.91s in there, you could try
3.91x1.67x12/6.06=12.93 and 12.93x2= 25.8" tires, which might look a little odd. Therefore lets go with 28s and see how that works
3.91x1.67x12/14=5.60; and that's a bit of a stretch, even for a 440.... but lets continue.
The ratios in that box are 3.09-1.67-100-.73od.
Lets try it with the 3.91s cuz they are already in there, and with 28s.
Ok so your first gear starter is 3.09x3.91 x12/14=10.35 corrected to a 24" tire. This is plenty of take-off power. So off you go and let's say you pull the stick at 2800. The Rs will drop to 2800x1.67/3.09=1513.... has that motorhome 440 got torque down there? I bet it does. So now you are at 19mph.
So now you boot it up to 30mph in second and hit 2350 has your 440 got torque there? I bet it does. So you continue to 2800@36mph preparing for the shift that will drop the Rs to 2800x1/1.67=1677 Well that would be a long hard pull to 65, so lets drive it up to 48mph@ 3760. Yeah that sounds doable.
So now you shift into direct @ 3760x1/1.67=2250. Got torque? Well not so much now that the truck is starting to push wind. Is it doable? Sure, but not really a performance option. Really, second gear will get you 60@4700. Then into direct, followed by overdrive right behind .
So now you are at 65=2226, a good cruiser-gear, but when will you use direct gear? It's kindof an unused gear. Say the lowest rpm you might want to use direct was 2400rpm; that would be 51mph. And 65 would be 3050.
So would 3.91s work? Yes, but
Yes but,does the od-box suit your driving needs? It's not really a performance combo, yet it requires a minimum first gear rpm close to 3000, to pull briskly in second gear. So a different combo of, tire size and rear gear, might be more attractive. But you can never get away from the,IMO, very wide splits.