Well, the spacers will act like washers but they "may" still rotate with the lock nut/ cone ensemble. The skinny washers have a tab that sits in a channel milled into the axel so they cannot rotate, the spacers don't have the tab.
They are there for a reason after all.
If it was mine and I had no new thick locknuts I would try all the other options starting with removing the skinny washers, no locktite and working on etc, etc.....
Dropout adjusters- I moved mine after 30 years being in a frame without a problem, so........... get the screw driver out and twiddle gently.
If you're lucky I may have a pair of thick lock nuts you can have. Depending on a man in Belgium.
You'll have to wait till after the 5 September though.