Would you add two bungs for o2 sensors in each manifold or would you only add one sensor. Seems like two would test both banks of carburation. Another option, would you install the bungs further back in the exhaust system? Analyzing the a/f with a machine will give fairly exacting results.
Does the size of the bung matter? I just bought one for my GTO for an upcoming dyno day and they did not seem to indicate the need for one on each side of the engine for all 8 cylinders.