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I think your going to like that 4:10 rear, it's a great ratio for these trucks. You can still pull, but allows you to cruse at 60. Should be no problem finding a matching r&p for the front Dana 44 (new or used), much more common than for the HO rears.
While your tearing into that rear, now is a great time to weld in a pipe bung for a drain plug. That's the one thing they are missing, and with clean oil they truly last forever.
I'm putting my money on your noise being in the transfer case. Even after a total rebuild of mine, truck still sounds like it has a bad ring and pinion about to blow. As I said in an earlier post I ran the truck with Xfer bypassed during rebuild, so I know exactly where the noise is coming from. Looks like my next project is some serious sound proofing.
Keep up the good work on the project,
Tom