as Granddadd said, "measure twice, cut ONCE...."
yes, before you cut the barrel, whatever way YOU want to cut it and being its stainless, you should not have a lot of issues as to " fit & finish..." it will clean up quite nicely.....
mark the barrel where you want it to "end up " ( the length you desire)
,and when you remove ( unscrew the front sight) you will see how far back the hole is from the front ( the muzzle) so you mark a small line, this SAME distance right there, behind your 'mark'......now with a straight edge, you go from the "center" rear sight hole ( elevation screw hole..) and you center the straight edge to the "center' of the front sight hole, and you again, "Mark" where it crosses the line for the "set back " distance.....this will give you "top dead center..." of the existing holes , that are currently being used on the gun....ta daa......... 'now you can cut the barrel off, stay a bit ahead of your "finish" line, so you can properly true up ( sqaure) the end of the muzzle....there are barrel reamers(muzzle & crown, combination...), with a plug for a true "perfect" muzzlem but they are costly, Brownells has them , maybe Midway too, or Mittermier???but why spend extra money for something you may NEVER have a need for anymore.....we just use a jig (fixture) cut and file down to the face of the fixture and its done and square.........you can cut a crown ,by hand,nothing fancy, its NOT a " match competition target firearm....." :wink:
drill ( a number #31 drill bit) and tap the hole for the front sight using a 6x 48 tpi ( thats what we use for MOST gun stuff...) Ruger may use a 6 x40?? not sure, never bothered to measure one really........the other is MORE "common' for guns ......drill the hole, using a "depth" gage(stop). so you do NOT drill through...you can always have some machinist do this part of it for you,....every one has a "machinist" in their family ( or a neighbor??) don't they?? ( don;t take it to work and have the boys do it as a "government job" someone may get fired for bringing a gun to work...) 8)
anyway, not that hard or complicated,this is NOT "rocket science"........lots of guys, who are NOT "gunsmiths" have cut down and shortened barrels over time. some do a nice job, take their time, and others "jury rig, (Bubba) or do a "schwak" job....hacksaws & pipecutters.
OR you can hire a gunsmith ,pull the barrel and have it turned down in a 'lathe', and pay for all of these steps ( operations....)
Good luck.................