When I first built my US-version '74 GTV with full euro setup, I only had to trim the vertical flanges on the chassis-side air funnel a tiny bit, and cut back the air horn on the air filter by about 1cm, from memory. It really wasn't a big issue. I don't know however if there are different versions of the later euro air filter housing (the one with the forward facing air horn, I'm ignoring the 1750 or RHD style).
PS the car is on spica now again.
Alcala de Henares, Spain