Wideband AFR tuning help.

So I am tuning my 340 with a wide band afr and have
a couple of questions for you guys that use them.

I have two different carbs I have been going back and forth on. A 3310 750 and a 670 Street Avenger.
The 3310 has 72's in the primaries and the 670
came with 65's. The 65's are way too small as at
cruise I am running about 17. The 750 at cruise
runs about 13.5

So given that here's the couple of questions I have:

Will advancing the timing change the afr to become
more lean? I am putting 68's or 70's in the 670
to richen it up, but will also be advancing the
timing about 8 more degrees before once I get my
recurved disty back. I am not sure the 3 sizes would be enough, and am thinking the slightly rich
3310 might be about right on if the advance leans
it out.

Also, under partial and full throttle, I have always understood you make the most HP around 12 on the afr is that correct?

Thanks.