[SCOBRAC]

What carbs are you running? It is all a compromise. I like both carbs feeding both the front and the rear of the engine. I most certainly want both carbs working off idle 1500-2500 rpm. But then I run the 450 cfm holley's.

Ford for homogenation purposes Ford went a little nuts with the carburation on the 427's and some 428's. The reason being you needed to run the same carb/intake that the OEM supplied. That meant you had between 1300 and 1500 cfm at your disposal.

Awesome for turning your 427 7000 at Leman. A little excessive for driving your fairlane to the dairy queen. The front carb will feed the entire engine and will do a fine job provided it is a 650 cfm+ unit. Most guys run 600's list. 1850 carbs as a substitute. those will also feed a 427 but not quite as well. The back carb should be in by 2500 and you should check that it is free to open by at least 1/4 throttle and be sure it can open to full throttle as well (you would be surprized how many can't)

As for progressive (what you had) and non progressive (what you have now) if you are running 600's you may want to calibrate the secondary diaphram spring to inhibit bog at WOT. if you do not have a bog you are lucky, the only drawback will be your fuel consumption. remember though, a vacuum seconday carb will only draw what it is asked to draw. despite having 1200 or 1400 cfm capacity if your engine is only able to use 850 cfm (and it is) your carbs will only put out 850 cfm.