MG had dropped out of the standard motor market by the time I got going properly in it ('93) but I remember doing a local inter-club between Swindon and Basingtoke in '89 and you could see that the further up the grid you went the smaller the pinions were...
The fast guy from Swindon (Andy Langdon) was an MG driver and from the pinion he had on and the speed of the car I'd be pretty certain that was one of Mick's 'special' motors