[Graham]

If you make the standard cars not at all standard, then you kind of invalidate the reason to have separate classes.

But they're not standard are they, as you can change the guide, wheels, gears (but not gear ratio), axles, axle tubes, bushings and interior

Yes class A is a modified Standard class. In general I believe that an entrant should be able to upgrade the standard model with running parts of the cars which (as we know are quite variable) with equivalent better functional parts.