A 351 already starts larger than you can make a 302 into. If you ever see the insides side by side, Ford put a lot into the 351 to beef it up to the task. Some racers don't like it, too heavy. But if you want reliable easy torque that will last, the 351 has the foundation for it. And room to go even bigger!
General guideline for me is 2000 RPM at 60 MPH. Some leeway on that. If you have a lot of drag (aero, rolling, etc), a little more RPM is fine. If you have light weight, little drag, and ample very low end torque (V8 fox body mustangs) they can roll down the highway at even less. Broncos are not mustangs, they need a bit of RPM at cruising speed. I like to keep enough RPM that you don't force a downshift on every hill. I want just enough RPM to have the driving torque to get up most hills at highway speeds without a downshift.
If you were starting from scratch, I would recommend a little more than the 4.10 gears. But they are really close, close enough actually. Since you already put them in the front, just roll with it. Pretty sure the AX15 OD ratio isn't as tall as what I normally deal with as well, so a touch less axle gear than I normally choose. Yea, the 4.10s are sounding even better. Mu late model daily driver has a 4.3 first gear and 3.69 axle ratio, I belive that is really close to the AX15 first gear and 4.10s. That is a nice ratio. Usable in daily driving, skippable if already in a roll as well. Not too low for actual street use. If you ran 4.56 gears I feel first gear may put you into no mans land. Too low for normal driving, but 2nd is too high to skip first. The 4.10s look better and better the more I think about them.
