I did have a '56 with a 316 and I still have the dual quad manifold and carb's that were a part of that performance package Pontiac performance guru John Delorean insisted they put out to compete with the 265 Chevrolet Power pack engines. I'll do some checking. There is a engine rebuilder shop in Indiana near the Illinois line that used to be a home for old Pontiac blocks asking to be rebuilt.
Give me a day and I'll check with relatives who trade with that shop.