Adjustable reamers are OK , particularly if you have the seat post in hand.

I have used them from time to time, last occasion 27.0>27.2, took it out just until the post fit, perfectly.

Best not to be in a hurry..

I agree, with the BB taps, in the Bike shops I worked in,
We built up a few prestige name Italian framesets.
the builders leave the chasing and facing the BB, reaming fork crown and head tube
to be done by the retailer..