It depends on your air cleaner. Some will clear, some will need a drop base.
I've run my 340/Eddy air gap with a few different combinations, all with Holley carbs. Current carb is a Holley 750 DP. I initially ran it with a Mopar Performance air cleaner and no modifications, with no carb spacers. It closed fine, but after while I noticed that with the engine vibration the fins on the air cleaner would rub against one section of the hoods under bracing. Didn't really hurt anything, but you could see the finish on the fins were marred and there was a shiny spot on the hood bracing.
After that I swapped out the MP air cleaner base for a drop base, no issues. I added in a 1/2" carb spacer, no issues. I wanted to go up to a 1" spacer, realized it wouldn't clear, and went to a 2.3" tall K&N air filter element.
This is the air cleaner element I use now
http://www.summitracing.com/parts/knn-e-2865
I used a Ford racing drop base that I had to scavenge from a Ford racing 13" air cleaner kit to keep my MP air cleaner lid. But mancini sells drop bases for the MP lid now...
http://www.manciniracing.com/mara13aircld.html
This is a shot with the MP air cleaner lid, drop base and 1/2" spacer. After this I went to the K&N filter and a 1" carb spacer.