(88 days until the 2012 WHPSC)
I took a holesaw to the subframe today to accommodate the head tube. I wasn't thrilled by the thought of using a relatively coarse toothed holesaw on such thin tubing, but the material cut with no problems.
After punching the hole, I clamped everything down in preparation for welding.
Here's a closeup of the interface I'll be welding: