Look it up on the cub cadet parts lookup site.
https://www.cubcadet.com/en_US/conte...8746fd66db39/y
I came up with IH-491489-R2
Are you SURE you have a 42" deck and not a 44" stamped steel deck??
Are the ends of the deck cast iron parts?
Got a picture?
Flip it and measure blade tip to blade tip for the correct size