570 or 670 Holley Street Avenger? Tune current one?

I think it's time for a new carb. Either that or a rebuild and some tuning. What do you think would be cheaper: rebuild and tune my carb or buy a Holley Street Avenger? If you go with the latter, what would be better for my setup: 570 or 670? Thanks!

mods are as follows:

'84 Mustang GT- Select Performance AOD, 2800 non-lock up torque converter, hardened input shaft, B&M SuperCooler, Holley 650 Vacuum Secondary Carburetor, Edelbrock Performer RPM Air Gap intake manifold, Edelbrock Performer 60329 aluminum heads, Edelbrock Performer camshaft, FRPP 1.6 RR's, RFPP underdrive pullies, Hedman shorty headers, BBK o/r H-pipe, American Thunder Flowmaster cat-back, MSD 6A, MSD Blaster 2, MSD Starter Saver (-20 degrees), MSD distributor, Holley 110 GPH electric "blue" fuel pump, Holley fuel pressure regulator, 7.5 rear w/ 3.73's. 2952 lbs.

:spot:
 
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I would probalby rebuild and tune your current carb. I had a 670 Street Avenger on my current setup and it was too big of a carb, always ran rich. I tried jetting it 6 or so jet sizes with no avail. I ended up getting a 600 CFM, plugs have always been light brown since.

Although, you are running a much better breatheing setup.

I would probably rebuild what you have and jet it up/down a few sizes if necessary. Have you checked your plugs? are they light brown, black, white? This will give you an idea on how well the carb is to your motor. Granted, the carb has to be in good working order before you 'read' the plugs, it can't be flooding or anything.

Holley has a calculator on their website to tell you roughly what size of a carb you need.