Markus,
I have zero experience with modding a pull choke carb, but have wondered about the very same thing!
Seems to me that the main restriction in the carb is the pull choke itself! The support piece that goes across the inlet would need to be thinned down. I bet the old timers pulled the whole choke assembly out, plugged the back, and ported the inlet! Living in a warmer climate here in SoCal, I typically just remove the choke on the later carbs and pressurize the tank before I try to start it. A shot of ether in the filter often lights it off, but that is not normally necessary.
What mods are being done to the engine? No governor? What RPM range will it run? The old pull choke workhorse was able to support 5HP at 3600RPM!