I would get a jy dana 70, 40 spline axles and put ford ends on with explorer or crown vic brakes. 10.5 ring gear and no heaver than the 60....and it comes with .5 thick tubes. You could build this for about $900 if you get a deal on a housing with the gears you want.

I got my 60 for $75, it was 600 to narrow and shafts from Dutchman. Pick your locker/posi unit and gears, you may get lucky and get what you want from the yard.... Brakes were $80 for the explorer discs I got a 3.55 r&p for $55, real Dana, so with a little work you can get a real nice setup fairly affordable...that will be indestructible.
Tim