ring and pinion swap

Yes, the gears are the same but you can't swap the carriers. The 99 Jeep will have 29 spline axles to your 73 axle using 27 spline.

I don't think I would do a swap with used gears though. You will need to get the pinion depth and backlash pretty much the same as they were in the Jeep or risk having a noisey rear end.