You guys are the masters at confusion. You've totally lost me in your train of thought. Stith mount, Savage 99? How much simpler can it get. Today we have a myriad of scope mounting options. Back in the day, not only did they have fewer options, scopes were scorned in lieu of open iron sights. The average hunter had one gun and he made a tool out of it. They couldn't give a rat's a s s about modifying a gun to "make it work" for them.
So let's get back to the Stith. Luckily I traded a mod 55 Winchester. No not the lever,,,,,,,,,,,,the one they called the single shot automatic, for a Stith that was on a 99. It was the only Stith I had and I wanted others. I copied that one, I drew up some prints of all the parts and commenced to duplicate every one. In doing so, I learned the design intent behind the mount and in order to hold zero, EVERYTHING must be snugged up. That means the scope must be against the ledge in the front tube AND your eye relief must be correct. Lyman and Weaver and the Norman Ford scopes seem to fit well. But now try to mount in a Leupold or Redfield, as well as others and you run into length issues. That scope MUST fit in the front tube against that ledge or the whole assembly will shift around.
I solved this by inserting a plastic shim between scope and ledge. I made shim of .200",.300", .400" and .500". I have yet to have any problems mounting any straight tube (which I prefer in the first place) in any of my Stiths.