just touching, i find it best to hold the carb...not completely upside down but angle it until the float arm is not compressing the spring plunger into the valve...with the float pivot uppermost
does your needle jet screw into the carb body then...rather that pressing in like the one in the pic?
This is the type of our early ones too, they dont have an o ring fitted to the mixture screw so that's correct, they also have a small brass orifice (air jet) pressed into the carb mouth as in the pic, wheras the later ones dont
also there is a really tiny passage from the mixing chamber of the needle jet that exits into bottom of the venturi behind the throttle valve...engine side (part of the pilot cct)