I jut honed out the chambers with some 120 grade paper on a shaft, It is only a few thou and the finish leaves a nice key for the solder. It may have removed some taper but not anything that I would consider significant. I would perhaps have bored it out if I had discovered it soon enough!!
But then again perhaps what I did was for the best as holding concentric to bore it would be a bear.

I make the shoe lump parralel.

I don't do the brazing. I farm that out to have it done in vaccum so I do not have the specs you need. Open hearth has problems of scaleing and embrittlement/temper. I do not have the expertiese in this field to give me the margins of safety that I want. Doubtless it can be done open hearth and has been in the past, it is just a personal thing that I do not want to do it.
This next set are for the firm that does it for me to try lazer beam brazing on. It is new for them on these steels and aparently the heat spread is just a couple of mm's. Should be interesting.

Regards