IMO, rather than mess with the gun, I'd find a 125-135 grain bullet that it likes and load a batch for it. I know that
Bayou Bullets will size their 9mm offerings up to .358 on request.
Having that gun's POI is actually a blessing in disguise since it permits the use of modern bonded 125-135 grain JHPs for defensive purposes that usually hit low from fixed-sight revolvers. The reason I still use 158-grain LSWC-HPs in my .38s is that they hit to POA with that load, not because I think that load is more effective.