The Old Models and early New Models share "fit" dimensions. Things began to change after Ruger "adjusted" things to make the Bisleys more "universal" with respect to "any grip frame fitting any cylinder frame".
So, even though one can "adapt" a NM grip frame to function on a OM cylinder frame the appearance of such a swap may indicate some serious fitting to be performed to make it "right".
JMHO,
flatgate