This is a used mule drive from the front of a Craftsman II riding mower with 18 HP horizontal motor and 6 speed (3 hi/lo) transmission, model 917.255914.
It works well and I have mowed with it.
The bracket I think is part number 120542X / 108253x the idlers are each 677A451 and spin freely. Both are obsolete parts that can't be bought new.
Get this good tested unit for a spare or replace what you have! 3 available, all pictured.
They all work but some have more surface rust than others, one has a slight bend, but all good working units.