Voltage on 10-30R metal faceplate
You have grounds in the boxes.
So.

Buy two 14-30Rs
remove the 10-30Rs
connect the 14-30Rs
Smash the 10-30Rs with a hammer so they don't get re-used
place in trash or recycling.

Per comment about &quot;3-wire compressor &amp; welder&quot;: alternatively L6-30R Plus L6-30P for the cords, and cap the neutral while connecting the ground.
Outlet looks like a NEMA 10-50 but is only stamped at 30