With the gas pedal held to the floor, just verify that the center carb's butterflies are exactly vertical within the throttle bores. You can over rotate the throttle plate such that it goes past vertical and inadvertently chokes down the air flow through the carb. This over rotation can also result in a hung throttle so be sure to check for it.
Assuming that you're using the mechanical linkage that came stock on a '67, make sure that the linkage is adjusted so that it doesn't hit the firewall or hang up on the ballast resistor's wiring at WOT. Now's a good time to make sure all the factory throttle return springs are functioning properly. Also check the vacuum lines leading to the front and rear carbs to make sure they fit properly and don't leak! (Can't tell you how many hours I've spent trying to figure out why I wasn't getting full power under acceleration that was the result of a vacuum leak!
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Have fun with your tri-power!