MSA have ruled out List C tyres from Road Going classes but are legal to use on the road and will pass an MOTC. Many WSCC owners and competitors use these tyres for road and competition but under MSA rules it immediately puts you into Modified Specialist Production Cars category and have to meet S12 of the Blue Book. SSOT wanted to keep a class for road legal class that used List 1C tyres; hence WSCC Classes C, D, E and F but as the Speed Series is regulated by the MSA we are not able to call them Road Going cars. These are "road based"
Cars that were specific for competition and used slicks (WSCC Classes G and H) are also bound by MSA Blue Book Modified Specialist Production Cars S12 - these are non road going
So the real difference is that a WSCC "road based" (not an MSA term) is a car fit for the road (i.e. could pass on motc, could be taxed and insured for the road and competes in that state) and a non-road going is a car that is not road legal (i.e. slicks, could not pass an motc, etc.).
To add to the difference if a J12 Road Based car is used on the road and has MOTC, Tax and Insurance then strictly speaking it does not have to have an MSA Logbook/Vehicle Passport to compete in MSA regulated events. However some scrutineers do not understand this and it is probably wise to have an MSA Vehicle Passport.