Wow. Lots of info here.
I've run a lot of combinations. On the Cleveland I've found that more then ever, you need an integrated system in that you just can't change a kitty cat into a lion with just a carb change.
The Cleveland CAN respond to a mechanical secondary carb with no problem and you CAN get 800hp out of YOUR engine but the question is do you really want to?
More then any other component, you are matching the carb to the camshaft profile.
On a Boss 351, I found that a Holley 4779 aka, a 750 double pumper, along with a camshaft upgrade to a 237 @.050 and about a .580 lift cam worked great. A good solid 450hp or so.
The issue there is it will idle at 1,000 rpm and it's a 50/50 proposition as to whether it belongs on the street or on the track.
You are going to have lots of power with it. Not subtle power and you are going to pay for it in not so subtle ways.
A 700cfm Holley on an engine with the approximate specs of a stock Boss 351 is probably as hot as you want to go on a street car these days. A stockish 351 CJ, like came originally from Ford is a 600 or a 650 cfm carb car at most.
Now as Marlin suggested, IF you want to talk WEBERS, 2x4 735 Holleys on a Trans Am intake manifold OR EVEN a 2x4 Holley set up on a 428 I can't deny that I know something about those BUT you DIDN'T ask and so I AIN'T goin' there. Well, not tonight anyway. But then again, I'm not really a subtle guy to begin with.
You need to be VERY specific about your engine specs but a 600, 650 or a 700 is PROBABLY where you are going to wind up.
Oh. Incidentally. A Holley in any of these sizes is going to give you 12-14mpg even on just a CJ spec. The Webers on the other hand, unless you drive it like Steve Mcqueen in Bullet are good for around 22. I'll never admit to that. 
Sharky's suggestion sounds veryinteresting. That one I never tried...or at least not yet. Maybe next week? I'm a little busy right now. 