First, you did not say if they were hooked up together or if you have progressive linkage. If hooked together, that's the beginning of your problem - way too much fuel for a street car. If you do not have progressive linkage, get it. The second carb should snap open when the first carb is typically about 3/4 open.
The secondary carb does not need a choke, but it should be wide open, nothing closed or set at an angle. This will only cause the carb to run rich.
Next, if both carbs are identical, you are running the idle circuits on both carbs - too rich. The factory dual 4 set-up used a secondary carb with no idle screws. You only adjust the carb you run off of.
You should have vacuum secondaries on each carb, so they should open as needed and provide a smooth transition without bog or stumble. Your jetting may need to be changed as they are most likely set-up to be run as a single use and not for dual 4's.
Other suggestions would be an an MSD unit and hot coil. The MSD does what it is designed to do - multispark at lower RPM's which will help fire the plugs better. You might also try a step or two hotter plug for better burning.
Points or electronic? Either way, I like to run the spark plug gap at the factory .035, but it is recommended with electronic distributors to run .040" or more. I just feel it takes too much energy to jump the wider gap, especially if you are already running rich. I also run an 8mm wire but I went with an 8.8mm on my present build - I like the Taylor brand.
I would also play around with the timing. Don't know what cam you have or compression, but 8 degrees at the crank may actually not be enough. It may be retarded to help with pre-ignition, but with all the excess gas right now, I don't think that should be a problem. I might bump it up to 9 degrees and upwards into the 12 degree range, moving a few degrees at a time and taking out on the road for a wide open blast to see how it goes and listen for detonation (rattling). This is where you want to check your distributor advance curve and set it up for the best performance. Do a forum search as this has been covered in depth, and very well.
I once ran a 409CI that I built up not knowing what I know now. Had a big solid cam that shook the windows. I installed a pair of 460 Ford 750 CFM AFB carbs after doing a rebuild. I screwed in the idle screws on the secondary carb. Even with progressive linkage, the plugs ran rich and would foul. I installed the MSD and hot coil- it ran smoother, but still had fouling plugs. Engine had the factory Mallory dual point with no vacuum advance set-up to be all in a 2,500 RPM's. So I bought a set of those aircraft style 5/6 electrodes that JC Whitney used to sell. Never fouled again like the regular plugs. Car ran like a raped ape and because it was really over carb'd, would keep on pulling past 6,500 RPM's and never quit pulling. Gas mileage was 8-10 MPG's.
Hope that helps.