dmen:
It doesn't amplify, but it's a 3" servo arm so it moves the rod in and out 6",
I would expect the scotch-yoke to have a lot of friction unless it is very highly engineered. It is a sliding mechanism.
The Pantograph is interesting, but I think it might be hard to constrain it to purely linear motion.
If the pushrod is constrained by sliding within a tube then you just need to connect the long end of the pantograph to some convenient position on the rod.
...R