It isn't safe to use a 3-wire dryer connection.
It's grandfathered, meaning it was legal when installed (maybe!) and they don't make you update your house every code cycle. That is not the same as safe - if it was, code would not change!
However, you can't extend it in any way. You want to add a ground to that box, that's an extension and you can't use neutral for that, no. Neutral is not ground in any way whatsoever. That was the whole point of outlawing the practice in 1965 for most things and 1996 for dryers and ranges. The box needs to remain floating.
A warning about /2+ground cable for dryers and ranges. It was never legal to use /2+ground cable for a dryer circuit. The general idea in 1965 was that the types of cables legal for a groundless range/dryer connections (/3 no ground, #10 SEU) were going extinct, and so the problem would cure itself when stocks depleted. Nobody ever imagined people would get creative and use /2+ground cable, abusing the ground as a neutral, something Code never allowed. That would be insane, since dryers are entirely 120V machines except for the heating element, for commonality with gas variants, so the neutral carries real, live, no-joke neutral current. And a bare ground is not up to that task.
You can retrofit a ground, though.
You can run a separate ground wire to ground the box, per the rules in 250.130(C). #10 wire via any route to a junction box with #10 or larger ground going back to the panel.
This has an effect on the landscape. Presuming your dryer cable was legacy legal (so not 10/2+gnd), you now have a fully qualified 4-wire feed, same as if you wired it with /3+gnd. You can use it in the normal ways, including an extension to an EV outlet.
EV charging is not to be underestimated
for those occasional times when I need to charge 2 cars at the same time (my main EV charging will happen on another circuit).
Wait, what now????
On a 1940s house? EV charging is the harshest load a house will ever see, and you can't just keep dogpiling more and more load onto an old service. That will have consequences.
You need to start at the NEC 220.82 service load calculation. Note that dryers factor into that calculation as a 40% load, but EV circuits come in as a 100% load, treated more harshly than even HVAC.
Now if the numbers work, great… but if they don't work, we have options. As you know, EV stations can be adjusted to any charge rate, and what's more, they can adjust on the fly - either to coordinate 2 vehicles sharing a limited power allocation, or to follow the surplus power available right now in the panel.
With a Power Sharing strategy, you live within the Load Calculation, and split the power to 2 cars with two charge stations (EVSE is the proper term, they're not actually chargers). They dynamically share it among both cars; when one car finishes or is absent, the other gets the full amount. This is sort of like a valet showing up at 3 AM to unplug one car and plug on the other, without you having to do anything.
With an EVEMS / Load Management strategy, the station monitors what other loads in the house are using in real time, and sends the surplus to the car. This disregards the Load Calculation entirely, which means, it also disregards amp limits and you can charge as fast as you want, up to the limit of the service. You can have a 60A charging station on a 60A service, even. So with EVEMS, you solve the 2-car problem by charging at the Fastest Charge Possible and then moving the charge cord before you go to bed.
Cost isn't extreme, it typically adds $300 to the cost of a wall unit, but you have to choose a wall unit that supports it, such as Tesla, Wallbox or Emporia.
They don't really have stations that double-stack both EVEMS and also Power Sharing in the North American market, yet. Wallbox has it in Europe.
