Yup, that tube is part of the crankcase.  The carb slides over it and is held on with a clamp.  It shouldn’t be hard to make one and weld it on.  Is the carb there?

Not the best angle but you get the idea.

In my photo I was fitting a new replacement carb to the motor, a KA-37.  It came with a 70’s style 18-20 horse carb taped onto it. The lever on top is the choke and the throttle is controlled by the mag lever.  The missing link in the photo is slotted and connects to a rod which opens and closes the idle air bypass valve on the bottom of the exhaust manifold. It’s a round disc with two holes in it and it should be cleaned out as they like to plug up with carbon from running on the required 8:1 fuel mix. Some models might be slightly different though.