360 Carb input
It's difficult to get a mechanical secondary carb not to bog with an auto trans.
Why not go with a vacuum secondary? Like a Holley 3310.
With the cam and single plane intake on the 380 HP crate 360, it's not going to have very much low end torque and power.
You should have around a 750 CFM carb, a stall, and a gear to work with it.