Try connecting 12V from another source, even directly from a battery post, for a temporary test of the choke heater. You are probably loading down the ignition by grabbing voltage from there. If you have a multimeter, try checking the resistance of the choke heater from the flag terminal on the choke cover to the carburetor housing- - - - -it should read at least 10-20 ohms, so only a small amount of current draw is used to heat the choke coil. Yes, the voltage stays on the choke heater anytime the engine is running. Since you have an aftermarket 4 barrel intake, it's probably best to stay with the 2 barrel carb and adapter and try to work with it. I use a vacuum gauge connected directly to intake manifold vacuum when adjusting idle mixture- - - -turn each idle jet screw clockwise until you see a drop in vacuum, then back it out until the vacuum rises and stabilizes. Do the same thing for the other barrel mixture screw. You might have to do more than one adjustment sequence to find the "sweet spot". Once that's done, turn both idle screws about 1/8 turn rich (CCW) to assist in off-idle throttle response. The final adjustment is to the throttle stop screw to set the desired idle speed.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!