Help with Edelbrock carb. calibration

I wonder if anyone can give me some help with my Edelbrock 600 cfm #1400 carb. My '59 Vette has a 327 replacement engine with a 30-30 cam, the above carb and Edelbrock manifold. (All inherited from a P.O.) I'm having performance trouble with the range from about 700 - 1600 rpms. The engine runs rough and I think too lean, but then smooths out and runs well above 1600 rpms. The mixture screws were not responding properly and I couldn't get a good idle mixture. I bought a set of Edelbrock set up springs and replaced the stock orange 5" springs with the blue 3" springs and the problem improved about 80% I'd say! The mixture screws now respond, but I can't get the mixture at idle any richer than about 2%. At least I have the feeling I'm on the right track. The metering rods are stamped with what looks like
"10-690". but I don't know what that refers to! Assuming they are the stock rods for the #1400 carb, they would be .073x.047 metering rods. I'm wondering if replacing them with .071x.047 rods or .070x.047 rods would give a little richer mixture in the lower rpms and solve my problem. Anyone have any thoughts, experiences or suggestions?
Thanks,
David