What exactly gets in the way when combining 3dr upgrights, if they're simply machined for AWD driveshafts/hubs/bearings and larger diameter struts? I mean, there are aftermarket billet uprights that combine front driveshaft capability with 3dr-style (instead of later pinched bolt) track control arms, essentially resulting in 3dr suspension geometry. Keeping the roll center in check is a good idea, even at stock Cosworth ride height. The most likely combination is to run moderate camber and as much caster as an adjustable strut bearing cradle will allow so this may be a bit more of an issue.

As far as Ecoboost engines are concerned, I think the jury is still out. Now that the current Focus RS has been on the market for a while and Mustang people are making rather serious power, it doesn't look that bad, after all. They've come a long way from early Mazda MZR engines the block is based on, and while it's still an open deck design (blockguard, anyone?), 500-ish reliable BHP or even WHP isn't that uncommon these days. Cosworth's take on the MZR/Duratec subject, the YD, is atmospheric, which seems to have spawned from racing regulations instead of viability of building a decent turbo engine out of it.

A turbocharged 2.4l 9-10:1 compression YD might justify a "Cosworth" badge on the car, too...