Will a Edelbrock air gap intake clear the hood on a 69 mustang mach 351w? I will be putting a holley street avenger 670cfm dual pumper. Has any one notice a difference in performance between a air gap intake and a edelbrock performer series?  

I know this is an old post, but someone else might find some use for the info.  

Not 351W directly, but my on-engine measurements between a Performer 302 and a Performer Air-Gap 302 intake show them to be the same height.  Specifically, the air cleaner flange on a Holley ends up in the same place in relation to the manifold flange on the block.  What Edelbrock does with the air gap is sink the area under the runners into the lifter valley some.  That puts the runners in the air.  They don't really change the carb pad height.  You can check that for the various intakes at Edelbrocks web site - they publish the height figures.  As for performance, the Performer series is pretty much a light weight stock replacement.  Switching from a Performer to a Air-Gap and from an Ed 600 to a Holley 600 DP was worth .2 and 2 MPH in the 1/8 mile on our fairly mild 302.