In case anyone is thinking of upgrading the gearbox, I've done it now. Various factors pushed me back to a 380 and I got the close ratio straight cut one from Dave Ashcroft. It was a bit of a fiddle to fit, but it is beautifully made and changes sweetly. It does whine (not in 4th of course) but I like it. Open cars tolerate noise.
The speedo now reads low (50 mph indicated is 57mph according to the phone GPS)... I think swapping drive gears is going to be too tricky with the box in, unless someone tells me how
I am happy with it, and the car now goes and sounds the way I like it. I don't intend to tour in it, I think it might not suit that very well but it suits the car.... Aero screens and twin roll hoops behind headrests, stripped down look. About to get its Tillet B6 seats fitted

Terry