Wow, my powers of observation are ... not so good.
The second page does say something about the 103 - run a 15mm SHA Dellorto, 3 balls in the variator and use a 12 tooth sprocket? I think....
Cutting the piston sides open makes sense.
I don't know if I want to raise the exhaust port on mine- the side transfers are only 1mm ahead of the exhaust- don't want the exhaust to open before the transfers, right?