Rope trick
Hi Rob,
It sounds like you are ready for the "Rope Trick". You are in luck as the area your nutplate is located, is not hard to get to, you have good size lighting holes less than a foot away so this will be easy.
First drill out the nut plate with the sheared bolt still in it, if possible do it so that when it is free you can shake it out of the top end of the vertical stabilizer.
Now for some fun, take a length of safety wire ( 0.020 works fine) about twice as long as the distance from the end of the fin to the bolt hole you just emptied (about 2.5 feet long). Put a washer twisted on the end of the wire (end of wire through center of washer, fold wire back next to its self and twist about three turns) that will end up outside the spar so that it will not get pulled through the bolt hole. With a little work you start the other end of the wire in through the bolt hole from the bracket side of the spar and work it out of the first lighting hole(nearest hole to the spar).
Now you should have the safety wire going in the bolt hole and out the top of the vertical stabilizer. Make a small aluminum square about 3/8 inch to the side from any scrap you have and drill a # 52 hole in the center, it may be easier if you drill first and then cut the small square. Slide a nut plate on the wire so that the flat side is set to end up against the spar (wire through the center hole in the nut plate the same as the bolt would enter) and let it slide down the wire, now add the small square you made above to the wire and let it slide on some. Bend the wire back on its self and twist a knot in it so that the little square can not slip off.
Now you can pull on the washer end of the wire until you get the nutplate flat against the inside surface of the spar. Use a small diameter awl to line up the rivet holes of the nut plate with the rivet holes in the spar and insert a 3/32 silver cleco into one of the rivet holes. The nut plate is now where you need it.
Use two CCR-264SS-3-2 pulled rivets to secure the nut plate to the spar and you can cut the wire and shake the inside end out of the top of the vertical stabilizer.
It is simpler than it sounds and can be used any place you can fine both ends of the wire.
Good luck.
Best regards,
Vern