The displacement, all by itself, doesn't tell you much about the motor.
Who built it, and the quality of the parts used, are much more important. A well-built 1776 could make more power, run cooler, and be more reliable that a poorly-built 1915.
If you don't know much about these cars and motors, by all means have someone who does look the car over before writing a check.
The days when you could plug in a fresh, high-quality VW motor for cheap are long gone.
'Freeway flyer' can mean different things to different people, but generally, it means the car has 'longer' gearing than stock for lower revs at highway speeds. As Robert said, this is most commonly done by swapping the stock 4.12:1 ring and pinion gear for a 3.88:1. Highly desirable, but only if your motor is making more power than an old, stock VW.