High idle in Park/Low idle in gear

[70TWO NOVA]

Alright guys, I just installed a new cam, heads and intake.
The cam is larger than the previous on I had (not huge under 500 lift and around 250-260 dur. but does have a 108 lobe sep.) the heads did bump up the compression a bit. they are 64cc where my old heads were 76cc. The intake is an Edelbrock Performer RPM and I have a 600CFM performer carb.
Okay, the problem Iam having with this new setup is that in park the idle is around 1100 and in gear it drops to around 500-600 and almost dies. I have tried adjust ing the idle mixture screws and timing a little, but it doesnt really help. Currently I have the base timing set at 11 degrees BTDC (should I go higher?). Iam running the weakest advance springs and the vacuum advance is hooked up. Some other threads suggest that I may have the wrong convereter with this new setup and say I should step up to a 2200-2600 stall (I currently have a stock stall) I will probably get a higher stall convereter anyway, but was wondering if there is anything i can do in the mean time to make the car idle lower in park and higher ingear since i do have to drive it everyday. Should I set the base timing higher, change to higher tension mechanical springs, diconnect the vacuum advance?

Any help would be greatly appreciated. Thanks Guys