Interesting what you say Michael.
Definitely avoid lugging the motor but do get this rattling sound that is there from 3500 rpm upwards that doesn't seem to smooth out as the revs rise but will do some experimenting.
The car went back to Morgan for new barrels and pistons that completely cured the tappety sound i was getting and was told that it was not making any noise that i should be worried about now. A case of they all do that sir, still not convinced all it OK though!