They sell special plugs that fit directly into the thermactor holes in the back of the heads. You can also get bolts at any hardware store too, thats what I did. The size your looking for is a 5/8"  thread about 1" long. 
		
	
		
		
		
		
		
		
			
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NewEngland Auto www.baystategearheads.com 
-91 Mustang Coupe, ex 4cyl (sold) 
-99 F150, 3" lift, 35" Procomps, Magnaflow exhaust 
			 
		
		
		
		
		
		
	
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