The '42 would end up on the wrong side of the barrel and the little bridge at the end of the slot wouldn't fit over that sight blade. The '16 would again not fit over the blade but would be on the proper side of the barrel. You would have to go back to a 1790 something to have just an open slot but it might be better to deal with the sight blade.
Glad you asked that question! It is vital to the core of the hobby!
Fill that rusty canteen with apple cider vinegar, cork it, and leave it in the back of a cool, dark, closet for 16 weeks. That will fix everything.
Glad to be of service!
1. All guns are always loaded.
2. Never point at anything you are not willing to kill.
3. Keep your finger off the trigger until your sights are on target.
4. Be sure of your target and what is beyond it.