Best bet would be to get a disk brake conversion for the original axle, if you're wanting to stay solid axle. There really isn't much in the line of solid axles with disk brakes except for 4x4s. Only exception I can think of are some Jeep 2wds, and those will be too narrow and will require fabrication to make them work.
If you're looking for IFS, the 3 best choices that keep things inexpensive will the '73-'87 C-10, which will be a little wide, the '84-'97 C4 Corvette (no collector value, parts are cheap), or the '98-'12 Crown Victoria/Grand Marquis/Town car (common as dirt, reliable).