Jonny,
The Alfa built by Rich Manchen, now owned by Mike Cook, has a front tread less than 6" narrower than OEM using covered wheels. Bill Ward's Opel is OEM or wider, the Black Salt Bocar is OEM or wider using covered wheels. Other MS cars are Corvettes with OEM spacing. The ex-Turk Berkley and the Jack White Berkley are very close to OEM, certaintly not 6" narrower.
I agree that MS class is an excellent place to race. Many opportunities to explore different theories. As I mentioned before, to allow the class to change into streamliners again is not the way I would like to see it go.
DW