The nice thing about tuning the secondary opening rate is that you can use a larger carb without drowning the engine. Smaller carbs would work better, but 600s will do well enough. The rear carb should be your primary, as the front venturii will be closer to the middle of the engine, providing better mixture distribution. Dual carbs always have distribution issues, but proper tuning of the setup will provide excellent driveability. The Edelbrock progressive linkage is designed to tip in the front carb after about 10-20% throttle opening or so, and is fine as is for your street engine. A tip for tuning the setup without proper carb balance hats: use 2 vacuum gauges that read the same. Confirm that they are reading the same by first attaching each to the same carb. Then attach one to each carb, and adjust your idle mixture and speed screws until both read the same vacuum.