Explicitly setting rotation plane and selecting a value

I am designing a tilting plate to mount on my mill/drill. I wanted to use Grasshopper to vary the angle of the plate and at the same time vary the angle of a slotted bar to match a pin location in the top plate and investigate interference. I hope the Rhino drawing is enough to be self explanatory. I’m kind of proud that I got this to work. top-plate.3dm (351.4 KB) top-plate-slot-interact.gh (20.7 KB)
If you vary the angle of the top plate with the Angle knob, you will see the slotted bar follow the upper pin location. I got it to work by playing with the plane location of the Rotation block but I’d like to better understand how I can set the rotation axis (plane?) using the Manage feature of the Rotation block. You don’t set this in Rhino because you are working in a specific view. The other thing about my gh implementation that seems clunky to me is the way I chose the angle for rotation of the slotted bar. I used the Dispatch but had to use and Addition block to pass the values on to the Rotation block for the slotted bar. There must be a better way.
Any suggestions for improvements are welcome. I’m trying to learn how to comment my programs.