Eddy 1405 tuning advice

4spd,
You are on the right track: increasing idle timing. As expected, idle rpm increased. That is because the engine is making more HP from the extra timing. And your vacuum increased, indicating more efficient use of the A/F mixture. It may well need even more timing, determined by the method I described in an earlier post. A cammed up 440 that I fired up on Saturday needs about 40* for best idle. A veeeery big cammed 454 I helped with needed 55*.

With the increased idle rpm, simply back off the idle speed screw....& re-adjust the mixture screws. They work together. Adjust them together.

Once you have done this, you will have [ with the extra timing ], a smoother idle with more vacuum than what you had using less timing.
It is also ok if you have less than 040" of T slot at idle. I have never found it to cause a problem, & it leaves more of the T slot available to cover from idle to the mains cct.
I am betting your low speed cruise surging [~40 mph & under ] will be improved/cured...& you haven't touched the met rods......