LinuxCNC as 4th axis indexer controller

I want to control my old Tormach 4th axis with my Haas super mini mill but I can't afford a $10,000 4th axis. My plan is to trigger the 4th axis from Mcodes on the Haas and have the 4th index for every trigger like a standalone indexer would then send a signal back to the Haas that the motion is complete. I would write a gcode program on the linux cnc controller that waits for the Mcode from the Haas then moves to it's next position and then send a confirmation signal. I'm new to linux CNC so I wanted to ask if this would be possible before I do further research in setting it up. Additionally I would want an encoder attached to the 4th axis table that would confirm it moved to the correct position. Anyone done something similar to this?

I had thought about that but it seamed like it would be more complicated than setting up linuxcnc. I think it would take a long time to make the arduino controller have a user friendly interface for setting up an indexer job. To me the idea writing a simple gcode file with my angular moves sounds simpler.

unfortunately unless I spend $2700 on the macros option I can't send the moves over the rs232 port. If I could send the data over rs232 then I would opt for building my own controller. I was under the impression that that I could set up a simple Linuxcnc computer that has an input signal from the haas to trigger a move and an output to the haas after the move. From reading some of the Linuxcnc documentation this seams to be within it's capability without writing any custom code right? I just want to start the linuxcnc program before the haas program and have it wait for the mcode signal before it makes any moves. I'm not sure I see what would make the arduino easier considering that I would have to write the code.

Why not use beaglebone black running linuxcnc.