Tony,
BTW, thanks for your historic sites!
The spindle muffler mount in the exhaust stack may be a medium firm drive fit. It should be possible to drift it out with an appropriate drift pin. I'd be tempted to make a rest fitted to the exhaust stack, of pine or similar common wood, and drill to clear the spindle ends. (I don't like whacking on engines, particularly unsupported parts of them.)
It should be little different than drifting out a PAW piston (gudgeon) pin, but that is a one-way thing. I don't believe K&B oriented the mount spindle.
BTW, they used to sell Alu buttons to cap the holes left with the spindle out of the engine. Probably no longer obtainable, but some years ago I believe I simulated some with 1/4" Alu rod, sawn, filed and peened to fit.
Luck!