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The other thing to consider is what wheel you are going to run. You don't want a 10 hole in the back and a 6 in front, so you'd have to look for similar year front and rear axles.
You "can't" have a two speed rear axle with a 4x4. Oh sure, you can build it that way, but you will eventually make that mistake and tear the TC or at least a driveshaft out of it.....
Your front axle will have to match the low of the two speed.
you coul always go out and find a 2 speed brownie. it would just have to be before a divorced x-case. my dad has a 57 gmc 650 that came with a powerglide and a 2 speed brownie that had a 1:1 and a 2:1 gear. it was a rather odd animal, since somebody put a 307 small block and a 4 speed in it.