Aside from timing, an example of differing hatch types (and Hanno is right in that the round version is not so much a hatch but rather a "hole" with a canvas cover) and particular contracts pertain to two 1944 Chevrolets of which I own examples of both.  Trucks from contract PE-197-11 came supplied with square hatches while those from contract PE-197-12 came supplied with round hatches.  Both contracts have been discussed on this forum before (PE-197-11 C60L's were supplied with winches and PE-197-12 C60L's were supplied with 16" wheels.  Both contracts had "REL" (Research Enterprises Limited) tags on the rear inner of the cab roof.)  As a result it would appear that trucks could be "ordered" with a limited number of "options" based on what was deemed necessary for that particular contract.
		 
		
		
		
		
		
		
			
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				Ian
			 
		
		
		
		
		
	
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