The 4.10 ratio rear is the holy grail for us 3/4T owners. The other common, stock ratio is 4.57 (that's what I have). One of those should be easy to find, and is an easy replacement. Don't even have to remove your tires! Just unbolt the axle-centers and pull them out a couple inches (disengage them from the diff). Undo the yoke from the drive shaft, then unbolt the whole pumpkin from the axle housing. Don't drop it on your head or anything! Then, jack up the replacement pumpkin and reverse the process (you did get the whole pumpkin, right? Either it was good when you got it, or you took it to a shop for tweaking). Slide the axles back in, turning them to engage the splines. You may have to lift the wheel now to turn it to line up the hub bolt holes.
If you want a lower ratio, you can add an overdrive (My plan) or find an 8-bolt rear axle the right length from a newer truck with a better ratio and change the whole thing. That would give you newer (easier to service) brakes and would be a fairly easy swap as well.
Good luck with your hunt.
Current fleet (subject to change w/o notice) \'49 GMC 3/4-Ton , 60 Austin Healey Frog-eye Sprite (some assembly required), 2011 Dodge Avenger, 2015 Jeep Cherokee. No, they don't all run. My other ride is a (B737)no, (B767)no, A320.... Update... was Embraer E190, now Boeing B787. Knowledge is a wonderful thing, but ignorance means you don't know you can't do something.
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