dual quad low profile?

Your all screwed up on this AFB/AVS thing I believe. Lets take a look at this carb set up a second.

All square bore carbs are square bore because of the "In general nature of equal sized throttle bores. The slightly larger sized rears of the AFB/AVS do not make them slightly or totally spreadbore in any way at all. If anything, it aids in throttle response being better for the overall size of the carb. Also a reason for the T-Q and Rochester spreadbore carbs. Also the mid 70's and on emmisions levels.

Taking the top off a Carter should be at best a one time deal, twice if it's really off. The rods do the rest. Super tuning them may require multi takes at it. The rod has more control over whats going on than the jet does. Besides, it's only a few screws and a couple of clips. No big deal. You go through more for an intake. And thats easy stuff.

Small AFB's can be purchased new @ 500 cfm from Edelbrock, OE carbs can be as small as 400. Though hard to find sometimes.