The holder drops into the QCTP, and I've added a support (pic
here)for the far edge to rest against. It's only intended for drilling/reaming, so it shouldn't see any up/down forces, just end on forces, unless I somehow manage to issue an X move with a drill in hole.
To mark the original holes in the bar (the Z-axis didn't have enough power to sink the centre drill into the steel), I used G52 offsets as per
this thread. I still need to get stub drills in the required sizes to try things properly, and figure out how I'm going to code the gang tooling. Actually, I'll go and update that thread!