There is something strange, your serial number lands on a 200 (DFI) - 0T178500 THRU 0T598999
plus the first element of your serial# is not a letter but a number, O= non correct 0= correct
the real sportmaster gear case for a 200XS 2.5, ratchet part number, pin, and springs are on the picture.
But there is a lot of confusion in your description and gear ratio for the 2.5
are you making a gear case repair with parts from different engine size?