[bobH]

Whichever way you want. There have been a couple guys that I knew that were doing model A's, both gone now. Borg Warner or Volvo into Model A. Or, same into a later V8 diff adapted to model A. Your choice. I don't get your comment about 2 piece V8 driveshaft. Maybe you are questioning how the d/s mates with the pinion. And, yes, starting in late 32, the d/s mated via a coupler. No big deal. Perhaps that is the route you would rather take. But, that leads to figuring out how to put a Model A spring on a V8 housing. In my view, putting the B/W OD into the Model A d/s, would be the simple approach, and indeed, that is how guys have done it in the past. Several ways to skin a cat. Pick your poison...
(There is one exception, regarding what you call 2-piece V8 driveshafts... 39, 40 Merc used a driveshaft that did not have a coupler, but rather the d/s was one-piece with the pinion. If you are searching for V8 diff's, you could possibly run into one. Otherwise, you will find a coupler, late 32 through 48.)(In case you need to know, Model A through 34 are the same width, drum-to-drum. And, the so-called 40-style is only an inch wider per side -- 2 inches wider overall.)
As for the 'stub pinion' being put into a Model A diff, I don't know. But, there are many talented machinists that have created various combinations. There are guys that have adapted a later 35-up V8 center section into 34 'Bells', and have worked out the details. So, if you are that talented, nearly anything is possible.