The barrel contour isn't a problem.
Cutting a 0.358" bore, a 0.350" hole with 0,004"deep rifling, would remove all of the original rifling and would have new rifling cut. Remember that bullet diameter is measured to the bottom of the grooves, not to the tops of the lands.
Whoever did the work would know how fast the ROT was cut, as should the person who contracted for the work to be done.
