I would say for a street driven car those Champion 12's should be OK. The plugs look nice and clean but I think a 670 carb is just not enough. Also I agree with earlier posts, many times the surge you feel can simply be too much timing.

Ideally I would say go to a 750, if not, try 35 total timing and maybe 2 jets up in the primarys.

I run NGK 6's in a 11:1 440, equal to Champion 10's. I would recommend NGK V-power XR5's for you.