If you were right-hand drive then the exhaust headers wouldn't have to battle past the steering. You could get the detailed dimensions from a supplier of headers for Zetecs into 70's Escorts & Cortina's but not guarantee from diagrams that they would clear.

The hot-rod market over there is awash with talented engineers knocking up twin headers for V8's so surely there's a shop around your way that could build a set for your car (and only half the time and materials compared to a V8.

BTW - back in my younger days I would hanker for an Amazon to custom build. They are the spit for a mini Mercury and would take the low-rider style with ease. At least one was built in the UK, chopped and channelled 2-door with mock US chrome style front. I will search Google for some pics.