From this post.https://www.stovebolt.com/ubbthread...4-1-1-5-and-2-ton-trucks.html#Post725050
P-30... thickness of the I-beam axle end where it fits into the spindle is the same for both P-30 and 2 ton AD axles, About 3.050"...
The kingpin diameter on the 2 ton axles is 1.109", and on the P-30 it is 1.179".
What are the dimensions of these features on your axle?
Can you swap in an axle that shares these dimensions?
If so already or if you can bolt in an axle (from larger truck similar year or perhaps newer??) that accepts the P30 spindles then that is one disc brake method/option.
In my opinion chassis swap is a lot of work for usually a finished product that just looks odd. Particularly old trucks that are reasonably narrow set onto a more modern wider chassis.
Not that looks matter that much so long as you like it, but I generally like things that look as they should/did.