No post with pictures of a nice looking engine is useless.

Ignition and/or fuel is still where I'd be looking.

Real quick ideas again:

You could install an inline fuel pressure gauge at the carb which would tell you alot.

You could check voltage at coil + in both "start" and "run". If you find both key positions
have less than battery voltage, there's a wiring error.

You already tested for tight valve guides/'assembly hard to operate when hot' by turning the crank bolt
when cold and hot, and not finding much of a difference between the two.

It's all good, though. As long as you're having fun working on it together, keep at it.