Carb cfm with ported heads?

107 is better, still 10mph from where I'd think it should be.

Looks like a XE285hl camshaft or similar. I'd set preload on the loose side, maybe a 1/4-1/2 turn. Sometimes very hard to gauge when you start to depress cup. Spinning PR while adjusting help with feel.

Fuel pressure and flow when at high rpm? If it has a mechanical pump, that's one place I would look as a pinch point.

Putting a bigger carb on now is a waste of money IMO. It's too far away from optimized to make a difference.