If by higher float level you mean the float itself is higher [ with n/s closed ], in the E carbs it is lower.
The fuel level in an E carb is lower than what it was in the original Carter AFBs.
It should be higher on the 750 by the fact that the booster sits higher than it should in the venturii. Vacuum and air flow (bleed) is what raises the fuel level up and out of the booster but the greatest depression is at the smallest part of the venturii also known as the vena contracta. So if you move the booster away from the point of fastest moving air higher there's less signal so the air flow has to be greater before you get enough vacuum present to lift the fuel. The vena contracta is at different heights on the 600 and 750 so require different length boosters. They skimped and only used 1.....the 600 for both.
800 looks to be fine. As a matter fact Joe Sherman stated he used them on engines up to 550HP and they got better mileage than a Holley.
