[Gaz64]

The EMPI comes with 3rd hole progression and larger fuel bowl capacity, as the major differences.

If a 2 hole progression IDA runs well enough without the dreaded "flatspot" then, the carb is probably a restriction to topend, small venturi 37 from factory.
An early starting main system with a small venturi might cover up the "flatspot" that many complain about when they end up with 40mm plus venturis.