I've used a mk6 Escort servo and master cylinder from a 1.8 zetec, I have the same brake conversion as you on my mk3 Escort.
You have to mod your servo brackets to get it to fit (not much, just elongate the holes and cut a few bits of them away) but it's well worth it, the pedal feels perfect and the brakes become even better

There are other solutions, I think someone said something about a series 2 RST master cylinder which will bolt straight on, but IMO go for the mk6 Escort servo, it's worth it