Rumor has it that the 1.3 piston is the same in every way but has a taller dome/crown for more compression, they say if you find those you'll be at 11:1.

I'm trying to avoid the vernier cam (but it is inevitable) because the 1981-1990 North American 1.6 and 1.9 are square tooth vs every other CVH ever has round teeth - and CVH vernier cams only come as round tooth except one extremely rare Ford performance cam sprocket. Which wouldn't be a problem but the 81-90 cars use an entirely different water pump than every other CVH so changing from square to round isn't easy.
Maybe I can take a stock one into a machine shop and have more keyways cut like the Motorsport cam sprocket I mentioned.