The Never Adjusts seems to be limited to the 12" Drums. You have 10" Drums(if they're 5 bolt) so standard issue applies.
Your existing Idler Axle should have Brake Flanges, so the Backers will bolt up.
Since you need a couple drums now, that will bring the tab up a bit.
Looks like 2 Drums, 4 Backers, Mounting Hardware, Brake Wire, Break Away Kit with Charger, Coupler, Heat Shrink/Liquid Electrical Tape, Butt Connectors, Cable Ties, and some Premium Grease.
Total tab should not be more than $500-$550, including tax, shipped to your door.
You may be able to do better by surfing the Harbor Freight, Northern Tool, Rigid Hitch, or Red Neck Trailer Supplies, of the world. Maybe E-bay?
If there's a Trailer Sales outfit close to you, it may be wise to seek council with them so you don't end up getting the wrong stuff. Measure twice cut once. They can get the parts, that you need, as well.
Not that tough of a task. Just a couple dollars, wrenching, routing, and buttoning up.
Been there, done that. It's what I do.