Hi, Asterix; Other than 'width', I don't know of another term, but it would be from the outside of each rear hub. As far as wheelbase, it is measured from the center of the front spindle to the center of the rear hub. Building a race car? I did the same with my '40 Ford Coupe....all Chev drivetrain. Lot of work, but a lot more dependable.
Good luck.
Loren