Andrew,
I used a longer screw all the way through the venturi, with a nut and washer on the other end. Much easier to make a venturi without threaded holes.
All the later Norvel .049/.061 engines used the same through screw arrangement, and there doesn't appear to be any performance penalty with any of these engines.
Better yet, order a venturi and spray bar from Jan Holuszko here on the forum, and use the stock needle, o-ring, and ratchet spring from the AP carb.
Bill