Mark,
Nice to see you online and getting your questions answered!
In an attempt to simplify your search - and glossing over some of the more trivial difference - what you'll find is that more recent traditional (Classic as Morgan call them) Morgan sports cars fall into 3 distinct groups: -
4/4 - smallest engine - in recent years a 1.8 (sold under the guise of the 4/4, Runabout and 4/4 Sport). Taking the standard model aside, the variations like the Runabout and 4/4 Sport simply offer different packages and levels of trim.
Plus 4 - 2.0 engine
Roadster - V6
