383 Wont Idle with new to me 800cfm DP. Idles and runs ok with Edelbrock/AFB

FWIW here's how I see it.
There wayyyy tooo many variables in the testing so far to begin to guess whether this carb has inherent problems.
A bigger carb should make more power and torque at WOT starting around 2500 to 3000 rpm and be most noticeble in the 1/4 mile.
But bigger primary throttles and venturis are more sensitive and difficult to tune for idle and low throttle than smaller throttles.
This difference alone, may or may not explain why the 600 Eddy is more streetable out of the box than the 4780.
It certainly plays a role in making the 4780 more difficult starting point.

So the question for you (340dartly) comes down to how committed you are to a steep and somewhat long tuning adventure.
We've done our best to provide some idea of what work, tools, time, knowledge and discipline will be involved.
If not, then a carb with smaller primaries is going to be easier.