Rear end ratios....What can I really change mine to?

[65Guy]

well with a gear that short you problly have a series 4 carrier which is the part that the ring gear bolts to. the lowest you can go with a 4 series is 3.73. if you want to go lower you will have to change the carrier. and im pretty shure any thing from a 65 all the way to a 87 if its truck 12 bolt it will fit, and if it is all stock you might consider blowing it all apart for a full rebuild. Bearings and seals.

[Captainfab]

What you have is the Eaton HO52 differential. The 4.57 gears are probably the most common gears in those differentials. There are no aftermarket gears available for those. The tallest gears that were available for those differentials were 4.11's. I know you said you didn't want to change the whole differential, but that is the only way you are going to get 3.73's. I would recommend going with a '73 and up 14 bolt. They are a very tough differential, can be found with 3.73's, and parts are easily found and not expensive. Parts for the HO52's are getting harder to find, and when you do they are $$$$$$.

One other option would be if you could find a Dana 60 in a '67-'72 C20. That would be a bolt in, in your truck, and better gears available.

Didn't you buy a set of 14 bolt trailing arm mounts from me a while back?