I know (?) the Mark II slabsides were all drilled and tapped...were ther others? How about the Gov't. models? the 5.5s? For some reason, scopes seem to help my old eyes!!
Grantcut
later on, we saw some either way, just use the Ruger base plate ( 3 holes) as a 'pattern', that would be good enough for us, and at least be in the proper way the factory did it...................
Ruger started doing the D&T operation on all their adj. sight models by serial number 225-82223.
Camfour began the trend in 2003 with a special D&T distributor model (MK512CA, Ruger model 0199, 302 made) in the s/n range 225-46986 to 225-57468.
Chet15