The results are in. I bought a 310x310 Ender bed because I could not easily get a glass plate matching the A350 dimensions. Some custom clips, firmware modifications, Slicer adjustments and modules crashing into beds, this is the result:
Leveling on glass:
Printed circle:
Probably a bit hard to see on the pictures, but it is not perfect yet. The “squish” on the filament is not completely even. Don’t know if I could have gotten it this flat by hand, though 
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