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Apparently not...the parts book shows a new number for the open differential when used on the 1 7/8" but not the Sure-Grip.



So then there must have been a significant overlap of the 742 and 489s. I say that because recently i acquired a 742 with a power lock date coded June 18 68. Which wouldn't be surprising I guess. Raises the question; when did the 742 cease?