All I can say is wow, huge thanks to all of you. This has been exactly the conversation I was hoping for.

You have certainly all given me a lot to think about.

1. Yes the seat post tube is anodized nicely and I would miss that finish
2. Given how common 27.2 is and that this is Tange 2 tubing (I.e., not paper thin) having it reamed is becoming more appealing... I really want to have the rear cantilever studs moved someday anyway to accommodate 700c, so maybe I should just have a builder do both at once
3. As is, the 27.2 post will insert maybe 1 inch into the 27mm seat tube but no further, both parts are exceptionally clean, so a ream or seatpost mod is definitely necessary to make these work together
4. Wonderful, wonderful suggestions on grits and methods. Exactly what I was hoping for

This forum is such an awesome resource. I'm going to think on it for a while before attempting anything... I'll keep you all posted on what route I take