It is NOT a balance tube.
The "two things" are the float bowls for the front and rear carb.
The incoming gas line hooks to the brass tube with the yellow cap.
Fuel is carried to the rear carb by the rubber tube between the two
float bowls.
The balance tube is part of the manifold. If you have the aluminum
manifold it runs across the top between the two carb mounting flanges.
If you have the cast arn manifold it is less visible but is between the
two halves of the manifold and probably has a steel cover plate on it,
held on by some 5/16" bolts.

The carbs shown in the pic are HS6 carbs. You may have the later HIF6
carbs which have the float bowl in the bottom of the carb body rather
than beside it. Performance is about equal. Both have problems but
they are different problems, and properly set up and tuned (assuming
they are in good repair) both will work very well.

Skinner Union has not made plumbing fixtures for a very long time.
(They haven't made many carbs lately either but parts are still available
both in Engle-Land (Burlen Co.) or the US (Joe Curto) or Canada (Rhys
at Island... in BC.))
--
George Downs, Bartlesville, Oklahoma, Central US