front end swapped to disks, what axles do i need to swap in so my lug patterns match?

I'll assume the front is now 73 or later front disc brakes with larger bolt pattern.
The 8.25 rear would have the matching bolt pattern.
With the rear having the smaller bolt pattern you have a 7.25 rear or a 8.75 rear.

7.25 rear with the larger bolt pattern to replace the 7.25 under there is one option. These are common and affordable.

8.75 rears are less common, more costly.
Wheel adapters ( 5 X 4 to 5 X 4.5 ) for either of the 2 rears is the very least expensive option. 2 adapters properly installed, 10 lug nuts, done.
1 spare , 1 lug wrench, happy moparing.

Most popular option for the more desired 8.75 rear is aftermarket axles with the larger bolt pattern. That requires changes in the brake drums also.