I looked at doing this to mount a bike carrier on the back of my 2011 +4. I had a look around and spoke to my insurer Gott Wynne and was told that although it was physically possible it was not legally (EU conformance stuff). I think however with your age of car it shouldn't be a problem.
What I managed to do was get a bracket attached to the main chassis rails (Williams) and then made a special rack to mount the bike rack.
Morgan Plus 4 - 2.5 Duratec Husqvarna 701 Enduro 1972 750 Norton Commando 4 bikes 2 tandems
