Mancini has the drop base that you need, but which one you use will depend on the rest of the air cleaner- they have bases for the stock unsilenced lids, as well as aftermarket lids. They're usually an inch drop or so.
And you can't run a carb spacer of any kind, either. MRE - "Low Pro" 13" Air Cleaner Baseplate MRE - "High Lip" Air Cleaner Baseplate