All I can say Heinz is that my observations match yours about the "wide" rear end of the 4/4 Sport. I don't think it's much. and I think it would be fixable. The front to rear wing overlap is variable over time and certainly before Superform, the narrow rear end of some Morgans produced a running board which was marginally wider than the rear wings, which always looked a bit "handmade" at that time.
If you can measure the earlier axle, drum to drum, that will give you the benchmark.
