rough idle on my 66

What intake manifold are you using? IIRC, the 4100 has some vaccum leak issues on some of the Edelbrock manifolds. That specifically cause a rough idle.
So along with timing, also do a vaccum leak check.
Also try a search, on the 4100, it'll bring up a lot of interesting information.

Has the car always had poor idle? Poor idle is caused by many things, but the two things that have bitten me the most are vaccum leaks and weak ignition. I'd check for vacuum leaks in all the usual places plus be SURE to check around the throttle shaft, if it wiggles at all, it's worn out. I've had carbs with over 1/8" of play in the shaft and the car still ran pretty well! Also, don't underestimate the value of a strong spark. My wife has a '69 Corvette that's all original and it hurts to run the thing in the garage, even with the door open. Even though it has a small carb (650 cfm on a 427) at idle, it's so rich it's not even funny. By comparison, my '68 has a pair of 390 CFM Holleys on amild 302 and runs very clean at idle, I beleive the big difference is the Pertronix ignition on the Mustang vs. the points on the Corvette. While it's very possible your problem may well be carb-related, at least make sure everything else is giving it a fighting chance.

The 4100 is not your problem because you have the stock intake. Try adjusting the idle adjustment screws. Take them all the way in, the out about 1 1/2 turns. Start the car and bring the right screw out 1/4 turn at a time. Once the engine smooths out, then adjust the left screw the same as the right. If this doesn't cure the rough idle, then I suggest you seriously consider a carb overhaul. You are obviously getting spark.
On edit: If after you get those idle adjustment screws adjusted and it still idles rough, try spraying carburetor cleaner around the base of the intake manifold. If that helps the rough idle, then your intake manifold is leaking.

Not to start a carb-adjusting war, but I don't think your method of idle mixture adjustment correct. For starters, backing the screw out feeds the idle circuit more gas, and while that may help cover up a vacuum leak, most engines will run pretty fat, yet still idle acceptably. I usually screw the screws all the way in (motor off), then back them out two full turns, then start the motor, warm it up, and then slowly turn the screws in until the idle stumbles. At that point, back it out a quarter of a turn and repeat for the other screw. Now the idle mixture is about as good as it will get. I've used this method with engines having one, two and four carbs and it has worked very well.