I think the Mk4 Escort only came with an 1.6 Diesel lump. Not sure if that was the same engine with less CC or a completely different layout.

Anyways, you can easily get 55 mpg out of an old Fiesta Mk4 1.8D. Mk4 Escort should be roughly the same weight so that's what you can expect there aswell.

If you did manage to get the newer Pug diesel engine in a car as light as a Mk4 Escort, 70+ mpg would be possible, I reckon.