Hi – since nobody’s replied yet, we’ll take the liberty of mentioning that there is a window specialist on the WSB sponsor team, West Seattle Window & Door:
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http://westseattlewindows.com/
We had all the window work on our house done when we bought it 20+ years ago – by companies that I don’t think are even in business any more! – so I can’t offer any direct experience, but WSW&D is local and offers consultations, so that might be one place to start. Good luck with your project!
-Tracy