Okay it looks like they have changed PNs from complete brackets to individual parts.
For both LH and RH you need two each 789-00368-4021 and 789-00455-4021. Cub Cadet yellow or change the suffix to -0637 for MTD powder black. You also need
four 5/16-18 flange head lock screws and 5/16-18 flange lock nuts. For mounting the mower frame you will need four 3/8-16 x .880 GR5 hex cap screws and 3/8-16 flange lock nuts. The only apparent difference between LH and RH is the way they are assembled.
Now if you want CC yellow you must order from Cub Cadet or if you MTD black from MTD. Stupid company policy they are the same group just different divisions. Also one color maybe sub for the other as they consolidate inventory.