Carl,

.360 Rook was essentially a low pressure cartridge similar to the .38 Long Colt revolver round.

The action would not have been designed for higher pressures and if you need to re-line it it would be sensible to look at cartridges from .38 Special (and not +P) downwards such as .32-20, .32 S&W long, .25-20 etc.

How is the original bore? If not badly pitted it might shoot acceptably with .38 Special HBWC or .38 Long Colt rounds.