Post or PM me those files please. Would be VERY helpful.
The skyfire PDB just pushes on the drawbar end. Remember that the belleville stack is significantly weaker on a BT30 than is requierd on a TTS system. much longer stroke required (I think about 4-5mm vs. .050") to release, but less spring pressure.
Honestly, the way to do the head bore without a big lathe or mill is to just grind it out in place by hand or use a jig saw. You only need 5mm width of cut, and just sneak up on it until the spindle just slips inside.
Step 2 is to clean the paint off the mounting surface and stone it flat.
Step 3 is to drill & tap the new mounting holes. Make yourself a steel bushing on your mill (before you get started!) and use that as a drill & tap guide.
Step 4 is to coat the spindle OD and flange with mold release or wax. And then do it again. And do the same for the mounting screws and threaded holes.
Step 5 is to grout the spindle in place with steel-filled epoxy. Set the spindle in a vise or fixture to hold it upright, coat the bore with epoxy and then lower it down on the head. Snug, but don't torque the mounting bolts. User a tongue depresser or whatever to get the gap completely filled and then run a 90mm O-ring down the spindle on the inside to kind of squish any epoxy back down in the annular gap - sort of like a valve packing follower.
Once the epoxy has set but not completely cured, tappy-tap-tap the spindle out and clean up any residue. Deburr any epoxy flashing.
You now have a better fit than would ever be achieved by boring - prefect transfer of spindle side loads to the head casting.
In fact, this is what I'm going to do after it's bored to a close fit - I'll grout it in with epoxy.
I've seen this done on big machines for precision surfaces, and also there are some good Youtube videos on it. I've tried it on a few things (my 4th axis frame plates for one) and am now a total convert to using epoxy to achieve good fits. Everything feel so much more rigid.
If you're paranoid about getting the spindle back out, then before you do it for real hit it with mold release or wax and the dribble a blob of your epoxy on it and try to pop the blob off once set. If it doesn't come off easily, try more release or wax.
And if the spindle gets stuck in there, finish the project and use the PDB to shove it out once it's mounted.