I don't know how soon you plan on doin' the swap but I believe the headers for the 1.8 are a different size than then the ABA. That would suck to buy a nice header and then have to replace it months later. Super expensive too.
What do you mean on the intake? You took the warm air cloth hose and routed it over by the fender? I think the only way to make it truly cold air is to block off the warm air intake all together cuz the flapper in the air box opens and regulates air temp based on expansion and contraction. That might be bad cuz the hole for the fender air is bigger than the warm air one and the flapper might never open cuz of the cooler air being drawn in. I wish there was a way to watch what that flapper was doin'. I always wonder how well mine actually works. It's about 25 years old.
I have CIS Lambda and I run all stock except a K&N filter and some Autotech wires. My first big upgrade will be a new camshaft. I'm thinkin' I'll run the TT266 with lightweight adjustable cam and intermediate gears. I'd like to do a full on exhaust as soon as possible, mines hurtin', but they're so expensive.