Get rid of the factory Model 15(predecessor of the Jeep Dana 35). That is what you have in an Eagle with a factory axle housing, and it has two-piece axle shafts(hub flange is keyed to shaft and held on with a large nut).
The front axle in an Eagle is kinda difficult to regear. There are different carriers for different ratios(similar to Jeep), but if you have a 2.35 gear ratio(common in Eagles that came with auto trans), ther is NO aftermarket or factory gear that will fit on the 2.35 differential carrier, other than the 2.35s.
What tire size will you be running? That's relatively important. Also, what are your build goals(like economy or offroad or maximum acceleration/fun)? Mine were the latter(autocross/subaru killer), and I chose 3.54/3.55 gears for my car. In order to do 3.54 front gears, I bought an entire front axle housing from a 4-cylinder Eagle, which came with 3.54 gears. The Eagle front axle housing is a D30, but it is not the same carrier as Jeeps, so I ran into an issue of not being able to install a traction device in it. I left it open, which is fine for the street, which is where my car is staying.
In the rear, since my car is staying on the street, and it is going to be running slightly smaller than stock(but much much wider) tires, I deceided that the later Jeep D35 would be fine for the street. XJ Cherokee rear axles( D35, D44, & Chrysler 8.25) are near bolt in to Eagles(not sure about the SX/4), but mine actually came out of a ZJ, so it has factory disk brakes with a parking brake setup, installed a Detroit True-trac full case Torsen(geared) limited slip. It is a C-clip axle, but I doubt I'll ever manage to pound on it hard enough to break a shaft. I cut off all the control arm brackets, and installed the leaf spring perches and shock mounts(same as XJ, available from Jeep fab shops like Rubicon Express or Rusty's Offroad). Still have to finish weld the perches, setting the differetnial pinion angle, and get a new rear driveshaft fabbed up. Also need to finish weld my AX-15/242 crossmember. Might be swapping in a ZJ 249 case, since I want the viscous coupler(a limited slip) instead of the 242's open diff. My reason for staying with the puny D35 is its light weight. The D44, 8.8, and Chrysler 8.25 are much heavier.