It reminds me in size of this Kayan parang described in a book from 1880. 
Like Ben I don't think the motifs of the handle is Iban but I don't know from which tribe it is.  
At the moment I am not at home with my reference library but maybe somebody else have some ideas on the snake motif tribewise? 
 
Michael
		 
		
		
		
			
		
		
		
		
		
		
		
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