i just did the same with my 235. i pulled the carb off of some unidentifiable truck as it was only frame and running gear the wrecker was using as a yard vehicle. anyways...
the threaded outlet is a direct link to the exhaust manifold. the one i got has a tube that is inserted on the top side of the exhaust manifold btween the 1/2 and 3/4 outlets. i brought it home and had to drill my manifold to make it work. plumb it up on the carb side and it works great. i remember it took a while to set up though...
1 more thing; to keep the condensation from freezing up my choke after repeated starts, i drilled a small hole in the bottom of the pot metal choke casing . took me a few cold mornings full of swearing to figure it out. you will not have a vacuum leak as that piston has at least one if not two o-rings in there, which draw tight as soon as the engine starts for vacuum break
