Better Performance Output

I Have a mild build on my 340 '68 Barracuda fastback with Summit Racing intake, 650 cfm double pumper, Pro Comp Heads, roller rockers/lifters, Speed Daddy headers with 1.5 inch tubes,. It ran 13.58 in the 1/4 mile with 3.55 gears. I had it Dyno'ed @318 HP to the wheels and roughly 300 ft-lbs of torque. I've upgraded to Edlebrock RPM Airgap intake which notably Increased throttle response/power and also switched out headers to Doug's with 1 5/8 tubing. Would a better carburetor help? What size is typically used on upgraded mild builds? Is 650cfm sufficient? Would a 750 produce more or be overkill, ....I noticed it ran rough with the intake manifold change and plan on another dyno tune.