Return line, can it be smaller than the feed line?

Looks like jpar is using the rear carb as sort of a primary carb and the front carb as a secondary carb. That front carb has to have the throttle pulled far enough to engage the U shaped bracket the adjustable stop.

Picture one is showing the adjustable stop. The further you move that stop away from the U bracket, the later it pulls the front carbs throttle.

Picture two he is pointing at the U bracket on the front carb.

Picture three looks like he is giving all of us the finger, or he is pointing out the rear carb hiem joint and how he spaced it out so the linkage is in line.

Picture four is showing his throttle cable mount.

So he is using progressive linkage. I never have used it because I always just let both sets of primaries open together and then the secondaries on both carbs open together.

With Holley carbs I pull all 8 barrels together.