What about a Kahles Helia 4S2 (fixed 4x) scope with the 4A, German #4 reticule and original brown leather scope covers would be a nice classic scope for your Rigby.
Good solid steel, reticule moving scope. Tube size is 26mm but some ring brands in this size available or 1" rings can be easily reamed out to fit.

A 4x scope any amount of magnification for the 350 and the older Kahles scopes had very good optics.