600 edelbrock secondary bog.
First, as no one ever addressed it that I saw, the metering rods/springs ain't got DOO DOO to do with the secondary side. NUTHIN. So lets get that out of the way. Vacuum signal too high? Yeah, ok. Whatever, AJ. IMO, your main problem is your gear ratio and those tall tires. It sounds like you are trying to "hurry" the carburetor and it is in no mood for it.
Try this simple experiment. Manually shifting the car, open the secondaries up at different RPM intervals. I say manually shift it so that the transmission will not get into a higher gear and lug the engine back down. I think that's basically your problem. The engine is simply not turning enough RPM to warrant a good, smooth transition into the secondaries.
So, try tipping the secondaries in at a higher and higher RPM and I bet you will find that the bog disappears at a given RPM. The engine is simply being lugged down to the point that the secondaries are essentially opening too soon. Try what I suggested and I bet you will find I am right.
Oh and one more thing. The 600 Edelbrock carburetors are absolutely the PERFECT size for almost any stock displacement MILD small block. Might be a little big for a 273, but you can make them work. On that 360, it is DEAD on the money.