I think the sizing calculators for carbs are a lot like the drag race calculators for cars. An interesting guideline, not to be taken to seriously. Real world conditions, in many cases, just cannot be reconciled with the carb calculations.
1200 cfm, all though a bit small, will work. 1350 would be 'just right'!
Seriously, it IS true that in plenty of cases for 'street' car over carbing is a common problem. I'd rather be 'rich' than 'lean' however.
During the GT-40 days when Shelby needed more horse power he went to a 2X4 setup. A single four is the best call for easier tuning and engine management, it's not always the best call for horse power.