The problem then is knowing what the local regulations are, it's very rare(if ever?) that signage will stipulate if keeping vehicle within bay refers to wheels or bodywork. As above, if there's a traffic warden about then you can ask, after all they are the ones who will give you a ticket, otherwise you either have to check with each council, or abandon parking. It would be very helpful if every council followed the same guidelines.
Anyway back to OP, I find with most parking bays the wheels on our 6.36m XLWB van just fit in the bay, and the LWB 6m vans have the exact same distance between wheels, so the only differance is the amount of overhang.