My first question is: Why is the 50 millionths degree of precison necessary, if you are looking at the cam lift/rotation parameters in Excell? Perhaps you are making this more difficult than necessary.
I have made all manner of cams using 4-axis CNC machines, beginning in 1981. Once the cam is digitized, in a series of angle/displacement readings, you can import the csv file into Excell, and see the cam profile.
When taking/recording the readings, you must be sure to sync the angle value, and the displacement. It may seem simple, but unless you have built a fully automated machine, it is easy to get the number pairs out of sync. For a simple setup, you can use a dividing head to hold one end of the camshaft, and set up a linear probe with spc output. Usually, a spc output has a two number output line, comma separated. The first one is a line count, and the other is the digital value. If you make note of the the start angle cam position relative to the starting line count, and advance the rotation exactly one degree at a time, you can edit the file when you are finished, and put in the correct angle values in place of the line count. One degree steps in an Excell file will give a very good picture of the cam. You will also have a table of offsets to whatever degree of precision your linear indicator reads to. Doing this by hand, you can digitize a cam lobe in about 45 minutes.
Making a dedicated machine would not be very difficult, and using Mach3 to do it is also not difficult. Mach could turn the rotary table in whatever increments you would choose, and operate a relay to clock the digital probe. The recording would not be done by Mach3, as it would be just stepping the rotary table, pause, clock the linear probe, step again etc. The linear probe could be sending it's readings to your laptop computer, i.e. a terminal program.
Regards, John