What size carburetor should I be using LA 360 engine?

What size cam? Duration wise.
Did you change (upgrade) the torque converter?

If it truly the carb, then you probably don’t have enough of the primary throttle blade open.

For a street bound driver, 670 is fine. What you can, but probably shouldn’t put up top is two different things. I can have tour car running and performing excellent with a 450 - 4bbl or a 850. Everything is in the tune and settings on set up. How well these carbs for you is another story on what you like. Or the car likes.

318WR is %100 correct.