Just saying: big heads, big intake ports, .490 valve lift and like 260 degrees duration, 8.9:1 compression . . . this should be a stout motor with a lot of high-rev power, and I'd expect it to be a little soggy off idle. Assume you've got a set of 1.5-inch headers on it.
I'm thinking a lot of valve overlap too? And I'm recalling Danny seeing over-rich low-end drivability issues at some point with his engine because he'd switched to shorter velocity stacks and there was like a cloud of atomized fuel hovering above both stacks... something like that.
All of which to say: hang in there. There are a lot of moving parts involved in a tune. You're absolutely sure you have the carbs synched? And the linkage is keeping them synched as you roll throttle?
My 2 cents (worth less than that, compared with Danny or someone else who knows something about carbs and tuning): 32 vents, 55 idles, 140 mains, F11s, 200 air correctors. Here's another guide, and another.
It does get easier as you get closer to perfect.