Some locknuts have a wrap-over cap that doesn't allow the steerer to poke through. These locknuts stop threading down when cap contacts top of steerer. I know for sure Campy and Tange headsets are like this. Not familiar with that vintage Ritchey though. As others mentioned, a washer or two between locknut and adjustable cup will allow locknut to press on cup.

Also trick with these old headsets is you want to unscrew the adjustable-cup upwards while screwing down the locknut. This provides more positive locking action than the locknut alone. So make an extra 1/16th turn tighter on adjustable-cup to allow for this unscrewing amount.

Would help if the OP posted some pictures of what he has. Assembled and disassembled.