Have a 70s Montgomery Ward Open Road 10 speed that I'm getting back into riding shape as a side project while visiting relatives for a few more days. The headset has me stumped though. It's got a smooth top race, some spacers, and then a locknut. Doesn't seem like tightening the locknut does anything. Any ideas?

Tightening the locknut should not change the adjustment of the bearing. Locknut must be loosened first to relieve pressure on the stack, then there must be a way to turn the top race/cup to make that adjustment and then retighten the locknut. Somewhere in the stack is an anti-turn washer with a tang or a flat that fits a corresponding indent on the steerer, and this washer helps hold the adjustment once complete.

There should be a "tabbed" washer to prevent rotation of the top race while tightening the locknut.

Is it possible that you've stripped some threads?

Perhaps pull everything apart and take some photos.

Typically the headset has a threaded upper race (cup or cone), plus an optional spacer plus a lock nut. Adjust the race, then tighten the lock nut.

Ah, the top race has some texture, so I turned it after loosening the locknut and that did the trick!

Remember that the correct bearing adjustment is only found after retightening the lock nut back against the upper race. So some trial and redo is typical to get easy swing but no knocking looseness. With the leverage that handle bars have over the headset bearings it's easy to over tighten the bearings and risk quicker wear. Andy