If i drove it reasonably careful which i may have tried for about 500ft
my 1.8 cvh on bike carbs was delivering about 38mpg before i destroyed it!
I dare say a carefully driven 1.8 zetec would return 40mpg if not more without too much trouble as these cars are so light, as already mentioned it would be cheap to source the parts and has been done by others plenty of times so is a straightforward job.