sounds like the only parts change that could be affecting this is a wilder cam & possibly how the untweeked carb is reacting to the lower vac/less stable idle. as said a vac leak is possible. can you set the initial at 17.5 (halfway between the 15 & 20 on the tab) & see if you can get a reasonably stable idle (as slow as you can get) & what idle speed & what the timing marks are doing. what springs are in the dist (OE light/heavy with elongated loop on one end?)