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.
Thinking of replacing drivetrain and chassis and researching alternatives. Wheelbase is the length between front and rear wheel hubs, what is the width measurement referred to as? Track maybe? The process of swapping in a new frame is generally pretty forward. Keeping in mind geometry, aside from (in this case) removing material from the rails the driveshaft would need similar modification but other than that? If all that is adjusted is length then the rest of the chassis components (suspension, etc) could possibly be used as is? I know this is a dramatic oversimplification but in theory is this close to the right idea?