That Kick down bracket appears to be for a 400, since it has the circle portion at the top, 400's had electrical solenoid if I am not mistaken, which is more of a plunger style, mine would have a cable going to carb linkage and then the bracket holds the cable similar to the throttle cable but opposite direction,

Spring is a throttle return spring, thinking maybe some of bracketry on the side of the carb may need changed... also to follow up on that... was it common at all at attach the throttle return spring towards the front of the manifold like some of the chevys did?

Thanks for all the feedback, I will post some pics of mine if I can...