Since you are adding DRO's etc for a third axis, why bother using Turn - you might as well just use another set up on MIll - it doesn't know it is running a lathe. All the DROs you want are on the page, and all the connections internal or otherwise are already made.
When you say you are motorising the tailstock, I take it you mean the feed in and out, not rotating the tailstock to drive the drill.
If you used the spare "y" axis and set up the steps per unit correctly, this can be directly controlled from GCode to feed in and out, and it would respond to all the standard GCode control.
I am planning a similar one with a turret so that I can centre drill, then drill and then counter sink work in the lathe - at the moment I have to change tools in the tailstock all the time. I shall run the turret on the a axis as a rotary axis , again with the steps per unit set so the one unit brings round a new tool.
Jim