Carb and tuning issues with new headers

My 68 cuda has a 340 with a mild cam, automatic trans and 355 read end. I just put a set of TCI headers on it with a new cross over back to the mufflers. I had headers before with no cross over. Car ran great. I had to run a lot of advance because of cam (I don’t know the size of the cam) and it did run a bit rich. I drive it on the street so it's a cruiser not a racer.
Since installing new headers and crossover I seem to be having some problems getting it to run smoothly. I have to also think the problem may be caused by the new exhaust system which is more efficient now. I'm sure it is in 1460 Edelbrock Carb and the timing. I have noticed the primary discharge nozzle has fuel coming out at idle. I'm sure that is causing the rough idle. Not to mention the back fire at idle and loading up.
I have purchased to tuning kit for the carb and have started working with the springs for the meetering rods. The edelbrock manual says to go with spring that has lower vacuum, but the says might have to go the other way.
I sure this is not a unique problem. I'm sure some of you have run into this. I haven't.
I sure would appreciate any ideas or direction.

Thanks
Steve