I guess that I don't understand the particular point that you are trying to make.

"Although I'm a fan of the TQ's I've decided staying with one is too much hassle for this application. Going back to a 500 CFM 2 barrel might be best but that would require buying an intake and a carb. At new prices that's approaching EFI throttle body injection like fitech, Holley, etc. So for this reason I am hoping to find a small 4-barrel (600-650 cfm) that fits the intake, is dependable, and pretty much a bolt on and go."

First: The OP likes the ThermoQuad style of carburetors.
Second: The OP wants "a small 4-barrel (600-650 cfm) that fits the intake, is dependable, and pretty much a bolt on and go."

What fits those requests better than the Street Demons? Your swap meet CarterBrock needing a 'kit' does not. Your example is apples to oranges.

You say you are happy with your CarterBrock. Two points on that: First you say your engine is modded. That is different than the OP's application and may, in fact, favor the CarterBrock. Second, have you tried a Street Demon to see if it is a better fit for your combo even though it is 'slightly modded'?

And lastly, Street Demons are on the bag for $100 to $400, you don't have to spend $500. So comparing an exaggerated new price to a swap meet price is again apple to oranges. And wouldn't you think there is a valid reason why the CarterBrocks are so cheap? Cheapest is not necessarily the best, especially when it comes to carbs and even more so when when the preference is for "a bolt on and go" carb.

Just another couple of thoughts.