Go to ebay and type in uni-syn into the search box and it will bring up many listings.
It will work on side draft carbs also.
As you can see in some of the photos, the balance tube rotates.
What Uni-syn does,is balance multiple carbs,
2,3,4,6 or twelve, the more there are, the more tedious it is.
On 2 carb set up, you could use 2 Uni-syn's, but swap them as you get into balance to check one against the other.
I believe John Lazenby's business started with this product.
Not listed in catalog, but John can help you
Ray Jones. Y'all come on down an see us. Ya hear?