Do the locknut up finger tight up to the cone for now and by the time you've tightened the track nut up against the dropout it should hold for a reasonable time and lessen the chance of your cone failing and spilling bearings all down the road. Andy has my cone spanners, inc 17mm, ask him nicely or offer him favours... or just use an adjustable wrench carefully.
Do the locknut up finger tight up to the cone for now and by the time you've tightened the track nut up against the dropout it should hold for a reasonable time and lessen the chance of your cone failing and spilling bearings all down the road. Andy has my cone spanners, inc 17mm, ask him nicely or offer him favours... or just use an adjustable wrench carefully.