Carter 750 float level

Some odd numbers...
5" of vacuum at 750 rpm sounds really odd. If the low vac is due to a big cam, would have expected to see a higher idle rpm.
Is the vac gauge accurate ? Are you sure you are measuring vac at the correct place? It needs to be below the t/blades. If unsure of the correct location, use the PCV port on the carb; you may have to neck down the hose for the reading.
What can you tell us about the engine specs? Auto or manual Trans?