Unfortunately....... not really the “right” carb.

It’s a “street” HP.

Does it have an easily adjustable secondary idle speed screw?

What size are the idle air bleeds?

How far out have you tried turning the mixture screws?

I’d also see what the idle vacuum is(my 383 with the 256-106 cam was around 6” in neutral @1200).
Also, 1000 in neutral is probably too low unless it’s a manual trans.

Do the leak down test before you go much farther.

I still feel like the 140psi is a big clue.