When using three carbs, progressive linkages are the way to go. Before you do anything, eliminating variables is the best approach. Is this engine already installed in a truck? Before you add the manifold with the three carbs, I suggest that you get the engine in good running order. No vacuum leaks, timing is good, and everything else.
The key to multi carb setups is to get everything happy with each other. I use a uni-syn tool and a lot of time. Start with adjusting the carbs with the Uni-sym tool to get a relative smooth idle. Then while the truck is running, I have further fine tuned the carbs by loosening the linkages while running and tweaking the carbs further.
Obviously, the more carbs you add, the more complex this operation becomes.
