Back in the 80s, tolerances weren't quite as good as modern bikes. Sure, high end bikes were generally good, but mass-market bikes could be a little off.
As the machinist says, if you can't make it perfect, make it adjustable.
Technique So on the drive side, the axle goes hard against the stop and is tightened first. The non-drive side will float part-way down the dropout as per your image. To get the wheel straight, stand on the left side of the bike and hold the rear brake on hard with your left hand. Use your left foot to push the rim below the chainstay so its centered there, and then use your right hand to tighten the NDS axle nut. This provides a triangle of reference to make the rear wheel straight in the frame.
As for spacers, yes they definitely exist, but in no way are they required. Some bikes use a small bolt through the rear of the dropout, but that's a weak point.
Surly have "Monkey Nuts" which are designed to sit on the axle like a washer, and fill the space. However you'd need to have exactly the right size. https://surlybikes.com/parts/monkey_nuts
Personally I find installation technique enough to hold the rear wheel. A QR wheel takes a lot more clamping force in this situation, but nutted axles like yours will be fine.
Consider that the leverage comes through the chain, so on the NDS there's over 100mm of leverage/multiplier that the drive side doesn't have.