I'd use an oven for the bending, a heat gun on that size of sheet will likely give less than steller results. 
 
170°C should work well for cast material but don't use a gas oven. For best results build a wood mold with the right curvature and place the sheet on top of it in the pre-heated oven. The sheet will form around it by itself. 
		
	
		
		
		
		
		
	
		
		
	
	
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