Ah ok. sorry. I think Micky1mo might be the guy to discuss BMW options with and Chris at Tribute should know his way around the MX5 enough to help answer your enquiry maybe.
As for the Triumph question . I don't think the Herald or Vitesse was offered as an auto , but couldn't swear to it.
Locally to me and only about 10-15 miles from Miglia is a company called Southern Triumph
www.southerntriumph.co.uk
The guy who runs that , Mark Swingler is an absolute fountain of knowledge on all things Triumph , he also builds modified versions of early TR's etc. including works replica's etc. He will definitely answer your question for you and a visit to him could easily be tied into a day trip to see the Miglia crew as well.