Sounds like the beginning of another love the beast story...
Can't go past the airplane wing indicator switch setup in the pre airflows.
The Escort rack and pinion conversion is a definite, if not the whole Escort platform, with GP4 rallying being so big at the moment theres some pretty serious stuff available, I'm using the Gaz gold coilover, dial adjustable struts in the Escort, they're monsterous in size and super high quality. Other than that even standard 2ltr Escort struts make the Cortina ones look like match sticks.
I use these guys for trim, rust sections and bolt ons, it costs about a hundred bucks to be a member but all they're stuff is as cheap as chips and good quality
http://www.mk1cortina.com/
Engine wise mine came with a 4age which was a pretty neat and easy conversion by the previous owner, I went back to the original pushrod because it also came with the car and made it a numbers match GT.
Zetec/ Duratec is a good option, the conversion can cost a bit but once you've got it the engines are a dime a dozen and cheap. They take boost too.
These guys will give you an idea of whats needed, they're just an example, there are other suppliers or you can fabricate yourself.
http://www.retro-ford.co.uk/shop/
They also do an BDA/ Cosworth style rocker cover for the Zetec that will trick even the purists if you want the oldschool look.
One mod that I've always looked at is moving the rear axle back a bit, don't know if its the same on the two doors but on the sedan the wheel sits way too far forward in the arch, might be worth looking at if you want to fit big wheels.
Good luck with it and sing out if you need to track down any odds and sods, its a bit underground but theres lots of Mk1 Cortina folk still out there.