In 1962/63 time frame, Ruger switched from the XR3 grip frame to the XR3-RED. The later one is larger, the earlier is a very close copy of the Colt SAA grip frame. The XR3-RED uses the same grip panels across old and new models; the grip frames are internally different to match the lockwork change.
With the safety addition to an Old Model, the trigger is now doing something else (sliding the safety off) in addition to the usual, so there's a reduction in trigger feel. It's usually not all THAT bad and personally, if I had an Old Model I'd run the safety unless the gun was a pure CAS/SASS game piece.