They’re are differences.
The Old Model grips from 1963 – 1973 and the New Model grips from 1993 – current will interchange on Bearcats, if awkwardly at times.
The red resin grips without medallions on the alpha Bearcats 1958 – 1963 are 1/8 inch shorter and the shoulder is cut with the radius of a 5/8 circle rather than an 11/16 circle like the OMs and NMs. OM and NM grips will not fit the alpha Bearcats. Alpha grips will go on OMs and NMs very sloppily.
On their revolvers with shoulders or washers, (Sec 6, Redhawk, Bearcat) Ruger came to embrace that 11/16 size, and I have wondered why that is. Seems like an oddball measurement.