My parts catalogue or my 03 V11 does not show the bolt or hole for the bolt. Maybe someone will have it and can remove it and give you the bolt dimension.
MGs have three (basically) different frames. #1 the loop frame. V7, Ambassador, El Dorado, Convert,etc. ,anything with a generator. #2 the Tonti frame. LM I,II,III,IV, I guess the 850T, T3, etc. anything with an alternator. #3 the spine frame. If you look at it it looks like a human spine.Framework hanging down loks like a ribcage. Your bike is a "spine frame".