I found a way to get the critical 3 wheels all done with the fence in one place and a super easy shim next to the fence.
For those of us who do not have a laser target on our drill press,
You might want to chuck up a fine point pen instead of the drill bit and let it mark up your wood as you fool around getting your "shims" correct. So I put the shim next to the fence and set the fence with the block and the cant angle rod in place and adjust to get the pen to come down and dot the back axle drill start to hit 1/8th above the bottom of the car. Now, the goal is to remove the shim and the angle cant rod, snug it all up and get the dot to hit 1/32nd above the back axle dot as suggested by John. Once you have this figured out, it will not be critical to set up future cars. They can be off on the back axle height a bit, but as long as your shim system puts the DFW up 1/32 higher, you will be good to go. You will need to move the fence for the last wheel in the air, but re-setup is fast with a solid shim system. You could add another shim so you don't ever move the fence, but once you get the critical height difference down , it is not a big deal to set up again for the next car. I have had first year Cubs set there own fence with using the pen, and then let them drill and they nail it just fine.