I finally had a chance to get back to this project and I'd generally state that the Youtube comment that suggested this would be a big pain in the neck was pretty accurate. This becomes doubly true when you've got a toddler to keep occupied.
Drilling a series of holes as suggested in Alaska Man's answer sort of worked, but not particularly well. Due to the ...
This, unfortunately, is a common and difficult problem. The issue is corrosion between the Aluminum and Steel and it can make it difficult and sometimes impossible to separate them.
Here is an article from Sheldon Brown that describes some causes, prevention, and fixes:
Sheldon Brown Seatpost Article
I suggestion trying #9 to start with.
I had the exact same problem and rather than removing the wood from under the counter, I totally removed the feet from the bottom of the washer and that gave me an extra 5/8". I put some thin furniture felt pads on the corners of the washer and it slid right into the space.
If that doesn't float your boat, the Dremel with a routing bit will be accurate ...
Those are grommets, not snap-rings or snap holes. Grommets provide a permanent ring providing an anti-tear resistance.
They are used to hang the tool roll from nails/hooks on a wall, for easy access to the tools in the roll. This would need fewer hooks than hanging each tool separately.
This is pretty rare in my experience, most workshops would hang tools ...