Hey Florida Phil, My engine and drive train are a carbon copy of yours except my block is a +.040 312.
I've tried a number of carbs including a '57 ECZ AFB, stock and re-jetted, 1.08 and 1.12 Autolites, stock and re-jetted and even tried mechanical secondaries. I also ran a 600 CFM Holley 4160 for a while which was the best seat of the pants of all those. I had a 735 CFM 4150 from a '68 Cobra Jet 428 sitting around, and on a whim kitted it and slapped it on. All I can say is WOW what a difference! I left the jetting stock and put the lightest yellow secondary diaphragm spring in it. Throttle response and idle are perfect. There is no hesitation. The engine just won't stop pulling, but I shift at 5800 or so. The part that I find hard to believe is that my fuel mileage is as good as any of the other carbs except the AFB which was only slightly better. 
I have a 750 CFM 4160 that I haven't tried and probably won't because the 735 is just plain sweet!
Go big, you won't be sorry!

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Interesting comments.  I have always gravitated toward Holley carburetors.  Most likely due to familiarity than anything else.  I chose the 1848-1 carburetor for my 292 because it is a copy of the original Holley used on the 312.  I am not disappointed in the performance of this carburetor.  It idles smooth and trouble free at 800 rpm even with the Isky cam.  I have zero flat spots or hesitations.   I am running out-of-the-box jetting with a 65 power valve.  My plugs are light brown and never foul.  The iron 312 intake manifold is a winner, especially considering what I paid for it.

All that said, who doesn't want more power at wide open throttle?  I wonder if a bigger 4V would be any better?  I have a 1967 GT 390 Holley 4V under my bench.  It needs a rebuild, but I may try it on my TBird just to see the difference.  Dyno tests are not going to tell me if it works better on the street.  Every engine is different as are the drivers.  We'll see what happens.

Phil, I believe those 390 GT carbs are only 600 CFM. 

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