Winchester 94's, or Marlin 94's? You didn't specify.
I have Williams and Lyman reciever sights on all my lever guns. Have had for over 30 years. I like them, they work supurbly for me.
I recently found out that for the new Angle Reject Winchesters, Williams makes a variation that attaches to the top of the reciever using the scope mount holes.
I haven't tried one of those, but I wouldn't hesitate if I owned such a rifle.
My early pre-safety Angle Reject was drilled and tapped for a side mount Lyman sight.
I have also mounted a Williams sight on a Marlin 1894 CS .357. It worked great.
As for using the original front sights, I have had no problems at all.