Just to add a little more info regarding the reason for the inquiry on the rivets. They don't appear to have ever been used to fasten something externally. I say that because they are tight and painted over long ago. It's Possible they are factory because of the precise spacing with four pair on each side. certainly looks jigged. One of the mechanics at the new garden field speculated that there may be a re-enforcing plate that runs the length of the elevator on each side.
The paint job on the plane is in good shape and I'm touching up spots. These are a bit of a challenge to deal with and not create a mess. Any corrosion cells left behind will of course come back through the touch up.
If they are not structural and removed then the bottom of the pop rivet will end up in the elevator internals and wander about. Sure would have been nice if they were aluminum like the thousands of other rivets and pop-rivets.
Any insights will be appreciated. In lieu of a viable solution I'll try to carefully remove as much of the corrosion as practical without doing more harm than good and touch up the paint.
Thanks much for all insights and thanks to marauder for posting this for me.