Ok, dont get uppity, this is going to be my opinion...lol. I think things are happening faster than you think in the carb.
The way it works is this: On all circuits except the power valve and acc pump, air flow (moving air) creates the energy to pull in fuel. At idle, the fuel is being pulled thru the idle circuit strictly by the air moving around the throttle plates. Think of the system this way...remove the acc pump system totally. Now, as your foot moves the throttle the air speed begins to increase thur the venturi(primary side). There is a small slot called the transition slot that is about 3xs the thickness of the plate long, stuck right where the throttle plates are at rest (idle). As the plates pass the slot, more slot is exposed to the airstream, and more fuel flows into the mix. When the transfer slot is completely exposed to the airstream, the only thing that richens the mixture is the power valve circuit, until the air speed has picked up enough to draw fuel out of the boosters. I emphasize air speed, because you'll always hear differeing opinions on carb sizing. But generally, the bigger the hole (throttle bore...) the slower the air speed for a given rpm. You have a large carb. 870 wet flowed is the equivolent of a 950cfm old school dry flowed Holley. It's 20% larger than I would ever say to run on a street 440. Now, add in the secondary detail. The secondary system relies on air moving thru the primary side to create the pull that opens the secondary plates. The spring counteracts this suction to close them and delay the opening. A lighter spring means less air speed is required to open the secondaries. The purple is one step lighter than the std (natural color) spring. If you couple the less air speed required, and the larger throttle bores with limited displacement, you will get a bog when you smack the throttle and the air spikes up then drops quick. In terms of elapsed time, this happens in hundreths of a second. The spike cracks the secondaries, then the spring has to close them against the now gone suction. The thing that's supposed to help all this, is the accelerator pump circuit. It's a finite volume. SO, the pump will discharge the same volume of fuel. The only thing you can change is how far the pump arm moves (the cam choice) and how long it takes to discharge that volume (the squirtor size). The smaller the squirtor, the longer time it takes to shoot the given volume of fuel (bigger hole, more goes thru faster). If you have a fairly mild gearing, and a fairly low stall speed (under 2500) then the engine's bog will get worse, not better unless you do two things. The carb is too big by most standards. But, it's vaccum secondary. So, I would go back to the 31 shooter and the factory cam, and I'd put in the next heavier spring from natural (brown I think?) to delay the secondaries. If you "feel" them open, you are only feeling them open and then the air speed pick up enough to deliver fuel at 3800. So they should be slammed shut with a heavier spring and kept there until the engine needs the air. If you go to the track, you would see the smoother operation result in faster speeds and lower ETs, even tho you'd swear it's not right. You should be able to run that carb, but it will need careful tuning to get things dialed in as good as possible.
