Which 670 Holley do you have? If it's a street avenger, I'd keep it on the shelf. I tried one on my 340 and it ran like crap. For engines with a bit of camshaft, the idle circuits are way too lean on those carbs. You'll have to open up the idle feed restrictors to keep it from bogging down. The 750dp will be a better carb for the motor IMO.