[weim55]

Here is what I recall when I had my hands in these things every day 30 years ago: your 1968 and possibly 1969 307 2 barrel has an intake manifold that directs crossover Exhaust heat up to the carburetor through a passage on the left and right front corners of the carburetor. The base of the carburetor is very unique and has a hollow passage for the exhaust Heat to transfer. These carburetors were notorious for corroding and failing in this hollow area. Vacuum leaks and idle problems are very common. They also use a very unique gasket and stainless steel metal plate that burns through overtime and causes the damage to the carburetor. I’m pretty sure GM abandonEd this set up and the exhaust passage to the carburetor in 1970. As long as you stay with the smaller 307 carburetor you should not need an adapter with the 1970 up unit. When I serviced these back in the day I would plug both of the exhaust holes coming up to the carburetor when I had things apart. If your intake manifold has these holes you will notice them right away when you pull the carburetor off, front corner left and right.

Steve weim55 Colorado