. . . of course, if these are precision bores, either in terms of their size, roundness, straightness,location, etc., the HDG can cause distortion. Maybe the bores should be put in afterwards?? (Sometimes not practical, however.)
We used to burnish our bores after glav. Mainly for a surface finish... it did not go well; we started using a high temperature grease for protection instead, and just machined off the galv
I guess the foam insulation didn't pan out.
You might look in to using "Cold" galvanizing paint with a bright zinc top coat to give it some shine.
Another option may be to powder coat.
Both allow you to mask off the bore.