Y'know, there are all kinds of Sprint Car groups out there; USAC, WOO, ASCS, MSCS, Must See, RaceSaver, and on and on. Wing, non-wing, 410, 360, 305, yadayadayada. I think Pappy Weld even built one with a transverse-mounted engine (I'm not going to call it a "Sidewinder, that'll go down a whole other rabbit trail). Was it chain-drive? Hmmm.
My point is, they are all Sprint Cars, because they share things in common; wheelbase, tread width, wheel size, construction practices.
using this logic I submit that a tube-framed, open wheel race car with a 60's to 70's inch wheelbase, 65 inch track on 13 inch wheels is a Midget. There may be other qualifiers needed to differentiate specific groups. But it's not a bad time to draw a line in the clay. Let the 10-inch wheeled sidewinders have Mini Sprint if they want it; we won't be needing it anymore...