[Lynn Eades]

Tom, Basically you need to reverse engineer it unless you have a good sample. Get your self a suitable bit of morris minor exhaust pipe, 763mm long.
The two outer holes should be about 732mm centers and are approximately on the same plane. This might test you a bit, plotting the other holes.
If you can borrow one, do so and make a jig to fit it, so that you can copy it. If not, you might put gear box and lever in a gear and with two bits of pipe and a bit that fits inside so that you can tack weld and check it for length and angle and use it for a jig when you have it sorted.
I hope that helps.