I have mine setup exactly the same as your drawing. 2 cross braces on both sides of the overflow is enough. 
 
Im guessing youre doing a bean overflow. I would put the 2 standpipes higher to have the top caps near the water surface. You'll need to put an airline on one of the standpipes.  
 
If I was to do it over, I would build an external or coast to coast overflow instead of the center internal overflow to get more tank space to play with. 
		
	
		
		
		
		
		
	
		
		
	
	
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