Any axle from the salvage yard can be swapped in if you ensure the GVW are similar, the springs have a similar contact point, and the driveshaft has a universal joint that can fit (a machine shop can do that for you if it needs to be done)
a lot of diesel medium truck brakes are either hydroboost or air-over-hydraulic, so interfacing the brakes won't be an issue.
An Isuzu axle might not be a bad idea as that will also address the issue of rims and tire availability that plagues the older medium-duty trucks.
