JR North fired this volley in
:

I also have hex keys that are driven with a 1/2" breaker bar or an
impact. I am really afraid that it may somehow break the SHCS, which
would be terrible considering its job (holding the mill head).

Iggy, those come out.

Soak them a couple of days in Kroil or whatever. Use impact-rated hex
bits. Support the head in case you break the bolts. If they all break,
it'll be easy enough to get the stubs out. You just don't want the head
tipping over unexpectedly.

Putting a pipe near the vertical section of an "L" key won't keep it from
twisting...

Same screws, same arrangement on my R2E4.

LLoyd