On the front of the upper intake manifold, there is a vacuum return line fitting.  That your PCV return tube connected to.  Plug that or you'll have a major vacuum leak.  I just use a large black vacuum cap.  I'd put a breather on the passenger side then, and plug the drivers.  It'll be like stock then, except you have a vented pressure release instead of a draw-through.  Mine is set up this way, with the stock valvecovers, and I have no problems whatsoever. 
		
	
		
		
		
		
		
		
			
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				'91 Mustang GT 5.0 AOD Daily Driver 
 
Current stats: NEW 302 short block,  E-303 cam (@.050, 220/220, .498/.498, 110 degrees), 1.6 roller rockers, Performer RPM heads (aluminum, 1.9/1.6, 60cc chambers), Cobra intake, Granatelli 75mm MAF, Billet AFPR, Equal-Length Shorty Headers, Off-Road X Pipe, Flowmasters, 4.10 POSI 
 
13.73 at 103.8, ~2.2 60'
			 
		
		
		
		
		
		
	
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