Fear of wrenching...

[OakLeaf]

I'm way way too scared to test it like the site suggests...

You'll be fine. Take a deep breath. Get a bright shop light and, if you need it, reading glasses or magnifying lenses. Shift onto the big ring (and if your shifters have a trim click, do that too). Now you're up against the H screw. If you can see the end of the screw contacting the stop, you're done (except for adjusting it to where you want it).

If the ends of the screws aren't where you can see them, observe the position of the slot or the Phillips star on one of them. Turn it out exactly one-half turn and see whether your derailleur moves. If the derailleur doesn't move, that's your L screw, so turn it back to where it was and try the other one.

It's a good practice when making adjustments that you're not sure of the effect, and/or when making adjustments that have to be the same in more than one place (motorcycle chain adjustments is what immediately springs to mind) to move by increments of 1/4 or 1/2 turn (or 1/3 turn, if you're turning hex nuts). Then you can go back exactly where you were before, if the adjustment doesn't work, and also you know you're doing the same thing on both sides.


PS my derailleur went back on fine... and it shifts fine on the stand... taking it out for a shakedown ride this afternoon, my first ride in TEXAS!


ETA: I read your post too quickly and didn't notice it was a late model Shimano derailleur. Shimano's website has technical data for most of their parts. The EV documents are parts fiches, the SI documents deal with installation and adjustment. According to that, the top adjustment screw is the one farther from the frame; with the chain on the big ring and small freewheel cog, there should be 0-0.5mm clearance between the chain and the outer plate of the cage.