Well done and good progress for you. I meant to say to remember to mark the gear before removal so the timing does not get upset. I had an engine where the timing marks will never align as it had the wrong model cam gear inside but same size and teeth number. Luckily I did make my own marks before stripping it down.
[/quote........oh yeh I've made that mistake before so yep the center pop was out doing its thing👍]

Yeah I agree they are one piece but I'm thinking there could be a shaft, maybe a taper one inside the extension shaft. I have one on an engine like that and come to think of it, it's a screw fitting. You turn the extension shaft opposite rotation and it unscrews. There is a thin threaded section that locks them together on the taper.  When the engine is running it's always tightening them although with a good couple of wacks on the pulley that sits on the extension, it breaks free and comes apart quite easily.  The thread is only about 10mm. Not a lot but it has no trouble holding 12 Hp.  Taper is the key i'd say.

I have no idea what this engine is like but mine has a stubby taper shaft for a gen head. The extension takes it back to a standard 3/4" in this case.

Might be worth a try unscrewing this extension? If it won't pull, that could be why?



Give the thing a few belts in the holes with some wood and a hammer or a soft drift opposite to engine rotation and see how you go.