After trying many options, I've finally found something that might work to reduce drafts and noise through these 1925 historic windows:
But that latch. Original brass, matches the house, but won't work well with the insulation. Is there a latch style that might be better available in a vintage style?
I went to the foam kerf style because the more modestly size rubber bulb insulation is so stiff it can't make for good compression, given the relatively wimpy single latch on each window. Sticky foam on the casing similarly failed because the gap ranges from zero to 1/4" or more. The window swings out on hinges.
Best Answer
Why not just add a piece of blocking behind the latch and move the latch receiving hole into the kerfed board? You could paint the blocking black or something that matches the latch hardware.