I had heard about this trick elsewhere and depending on what front driveshaft you get depends on what you can use it for.
You're going to be looking for the front shaft from an Explorer or a Ranger with a 1354 trans. You can get the flanges from the rear shaft. This mod works for BIIs with an a4ld, FM-146 or M5OD. If you have a TK-4, TK-5 or FM-145, the length will likely be wrong - those require a slightly longer shaft - which you might be able to do by leaving the double cardigan in place and just adding a flange.
Another thing that can be done (provided you can find shafts that both have coarse splines or fine splines) is to swap the front slip joint for a rear one (rears are supposed to be a little longer, IIRC).
For front driveshafts....
FM-145 front shafts are shorter (and thus about perfect for a D-35 front swap) than the front shafts in a FM-146, a4ld, and M5OD.
Front shafts out of a TK4 or C5 equipped Ranger/BII are shorter yet and will work for a D-35 swap in a FM-145 or TK-5 rig.