Mike,
I have a 54 engine on the engine stand so I measured for you. Under the exhaust is 1 5/8 inch and the front and rear are 2 inch. That is also what was stamped in the plugs so my measuring was pretty good. Remember, mine is a 54 but it was easy to get to. Any other measurements you need before it goes back between the fenders (probably another year).
Later JJ and 4
