Have a look at the 'Making it Feed' sticky in the Gunsmithing forum over at the Accurate Reloading forums.

That'll give you an idea on the work that needs to be done. Pretty common for Mauser type actions to need a bit of work to feed blunt RN's reliably. Even Win M70's, especially the .458WM ones.

There's bound to be a gunsmith in NZ that does this job well.