Boring a clone carb to the above mention bore needs to be done carefully at an offset from the center. If you don't you will end up breaching into the fuel circuitry pathways rendering the carb into junk. I would recommend going to a Dover or Nr racing carb because they have done all the trial and error work and know what works best. Really from a economic standpoint.
There is not much meat on the idle passage side and on the top side. Like said above around .670 you better be careful. What I have done is cut some out of the bottom and the right side before I start boring it. Then I'll straighten it up with a reamer. It has helped me gain some.