Dear EZ Cool and mid-60s Buick caregivers,
This post may be more at home in another category because its not Nailhead specific but since I started here I'm staying here.
No worries. On a small forum like this we will be able to find this information easily.
After getting much good advice from others I bought a Vintage air GTO direct fit unit for our '65 Skylark. In order to make it fit it was necessary to cut off some of the defroster duct. Instead of removing it entirely, which would be a big hassle, I opted to just trimming enough to clear then I capped off the bottom side then added a couple of tubes to hook the defroster hoses to. Not the prettiest job but its all hidden anyway.
Actually it is a much nicer solution than following the Vintage Air instructions and using their own ducting which is what my wagon has. Since all this is hidden anyway, it is the functionality that counts and the defogger will work better in your arrangement. Congrats and thanks for sharing!
Cheers, Edouard