Howdy again!
I. Will K., I have the RL Wilson book (Beautiful!) about Winchester rifles and yep, yer right about double dovetails on Henrys - there are several pictured in the book - to include the "Lincoln Presentation" rifle, ser. # 9. (see: p. 15 in the book) It has the sight on the receiver, but you can also see where the barrel has an empty dovetail - which surprises me. NOT that they moved the sight; I'm sure it's an improvment, but I'd have thought a VERY special gun like that would have had a sight blank in the dovetail to "spruce it up."
Will52100, if you do get one of the Marbles sight, one of the sight screws will fit on the receiver tang, but I think you have to do some work on the buttstock to make a spot for the rear sight base screw.