You could fit a conventional Mustang bridge to sort the spacing, but that would then necessitate drilling the body for through-body stringing, and maybe there is some additional routing under that bridge design?
I owned a MIJ Mustang bass and the pickups were weak sauce. I bolstered mine with neodymium magnets, simply to squeeze a bit more power out of the pickups. I looked at the Nordstrand pickups, but they were expensive and apparently made the bass sound like a P bass. If that is the case, why go down the route of a new pickguard, set of pickups, new bridge (potentially?), simply to get back to square one? For aesthetic purposes you could put closed pickup covers on the P pickup to get a bit closer to the Mustang mojo?
I'm not trying to be a downer. I've thought about the various mods you could do to these new PJ Mustangs. I liked the one I tried, simply because it didn't have the weak thump/twang of my old MIJ Mustang and sounded really authoritative for a shortscale bass.