Hey, I did have an A440f behind the 6 bt for quite a while. Most of the work was done by the PO or whatever shop he had it at.
I thought the A440 had a rodney's extreme valvebody kit but later when I went to sell it I couldnt find any markings as such. It did however have a custom torque converter from wholesale automatic out of of australia.
The transmission held up fine, but it started eating flexplates, which I suspect was more to do with engine/transmission misalignment than the torque.
I now run it with an advanced adapter to a 60 series split case, with a cummins nv4500 (sometimes known as the NV4500HD) which is slightly different than the ones found in gassers. I swapped on some 60 series front hubs ands run the truck in 2wd on the beaten path.
For the extra work involved getting the 5 speed NV4500 in there, I still would have preffered it done in the first place. I do like it over the auto, its easier to slow down, let it idle at different gears up and down hills, and is a little funner to drive.
If you do want to stick with the A440, go for it, but you may end up getting a custom torque converter. Also if you cant find an adapter and need one made, your cost savings over the NV4500/split case start getting closer.
If you really prefer the auto, or you want it a little more driver friendly for the wife, then maybe an auto is the way to go. There is some good info about 4bt/6bt swaps in buildups in the 60 series section and the diesel section as well. I have a few pics of some work in a thread as well.
https://forum.ih8mud.com/80-series-tech/407556-codys-slow-white-80-re-build.html
Cody.