The car is currently fitted with a jaguar Salisbury diff, ratio 3.54 which gives a theoretical top speed of 224 mph by my calculations, so I've had a hint around and there is a performance jaguar specialist that retro fits the newer ratio crown wheel and pinions into the older casings

Can get a 4.09 to give an approximate top speed of 192 mph which will be alot more suitable for point to point and drag racing, considering buying one so I have both options available to me
those speed assume 8500 rpm and a decent size tyre on the rear