Crystal malts/carapils will not have an effect on pH, so don't bother using them to "balance the carbonate". Acidulated malt, acid additions, or roast malts would, though, or RO water and building up would work too. You might also be able to boil your water and decant off of the precipitate or use campden tablets as well.
Wheat, carapils, and flaked barley all work well to aid head retention. I use a couple ounces of flaked barley from the bulk section at the supermarket myself with good results.
Not sure what effect high pH would have on head retention, but I doubt it would have any significant amount. What do others say?
Also, a zombie thread.