History of that dangerous socket
When they started grounding things in the 1960s, the appliance industry asked for a "pass" on dryers and ranges connecting via NEMA 10 receps (hot-hot-neutral). They were afraid a compulsory conversion to the modern NEMA 14 series (hot-hot-neutral-ground) would result in customer confusion and lost appliance sales. ...
Thanks so much for your response(s), guys! The box is in a somewhat hard to access place, so it took some time to figure out how to access it fully... no metal conduit, but... as I cut the old stucco around and wiggled the box... I found the ground wire jammed far back behind the box in the wall!! Yaaay!
If the motor winding is connected in STAR and the star point is accessible as in the diagram, you can reconnect it in DELTA. That will make it 240V 3 phase. Connect a capacitor as shown to drive the 2nd phase. The torque characteristic won't be as good though. Use the rated current on the name plate & multiply it by √3 to calculate the capacitor value. ...
You have grounds in the boxes.
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 "3-wire compressor & welder": alternatively L6-30R Plus L6-30P for the cords, and cap the neutral while connecting the ground.
Outlet looks like a ...
I thought I'd come back after this time and say that I decided not to go with a switch. I put a plug in the middle of the dryer power cord that I use to plug in a 10' 240V dryer cord. I only use the dryer once or twice a week and it runs for 20-30 minutes, so it has not been a problem. The breaker hasn't tripped once. I do appreciate all of the replies.
Yes, just be sure to run a 4 wire circuit (2 hots, neutral and ground), if the current garage is attached you don't need extra ground rods. In fact, since you are planning for the future, you might install a sub-panel now that would supply your EVSE outlet as well as other circuits in the future. As many others have said here, go bigger than you expect to ...