Depends on what "normal driving" means to you. FEs were never known for great gas mileage but they sure are fun. You could stick a 5 speed in it and squeeze a little bit more out of it.
It shouldn't be too bad w/355's , if you drive it "normal" most of the time .
I would think in the area of 10 - 12 mpg . Rear tire diameter will also be a factor .
I have a '65 Falcon Sprint w/289 4v that is a 4 spd . , and it's a ball to drive -
I would think that Fairlane would be too !