You'll find that ya can't fit the gun to the sight because there is only enough metal on the mounting "rail" of the reciever to accomidate Ruger's "half dovetail" mounting arrangement....and that if you postion the M1 sight against it, the front of the sight's dovetail covers the screw hole which originaly attached the folding-sight's clamping gizmo.
In other words, you're going to have to modify the M1 sight, not the gun.
Some folks resize the M1 dovetail so they can re-use Ruger's clamping gizmo.
What I do instead, is carefully use a very small rat-tail file to create a semi-circle in the center of the of the front edge of the M1 sight dovetail...just deep enough so that when the sight is positioned into the far-rear of the reciever dovetail, the factory screw hole can be viewd through the semi-circular cut I made. If done correctly, the old Ruger sight screw can be installed through the cut...which when snugged-down, positions the center line of the M1 sight body to the centerline of the reciever while also holding the sight in place....then.....I remove the sight, remove the finish from the bottom of it's dovetail by rubbing it over a flat piece of 240 grit sandpaper, remove the finish from where it is to sit on the reciever, "tin" the bottom of the M1 sight with soft solder, re-install it with the screw, and carefully heat the area untill the solder flows enough to form a bond. After everything has cooled enough to touch, I re-check the mounting screw to make sure it's snug.
Makes for a perty-solid mounting...much better than the "screw 'n clamp gizmo" that Ruger uses.
Other stuff I've learned:
The Mini-14 front sight is too tall for the lowest (100 Yd) setting of the M1 sight, so it'll need filled down accordingly....."accordingly" meaning to work right with whatever ammo you commonly use.
You'll also find that the elevation adjustments (yardage marks) of the M1 sight aint right for a Mini-14 and it's flatter shooting ammo, so you'll have to do some experimenting relative to what each click of elevation actualy means in yards for your particlar gun/ammo.
Hope this helps.
DGW