After talking with Eck, I'm almost convinced to go 4.56's with the ZF that I have sitting in the garage. I'm curious if anyone else has run this combo with a 33" tire? Looking at the grim keeper calculator and using actual tire heights, it doesn't seem to be a big difference between the 33 I'll run and the 35 that Eck runs.

There's a guy selling a 9" drop out with posi that was rebuilt at Colorado axle and gear that I'm thinking about doing vs rebuilding mine.

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What engine are you running?

As you noted the difference isn't that big-a few hundred rpm. The 302 likes to spin a little more than the 351w will. It mostly depends on your priorities. Do you want better fuel economy and modern highway rpms or a little more scoot and not having to downshift? For comparison, ill be running 4.56 with a 351w on 37s, assuming I can ever figure out why I'm having lean issues and drive the dang thing.

For sure. It'll be a big upgrade either way and 4.56 would give you some breathing room for larger tires if you wanted to go bigger.