I think you're barking up the wrong tree. Headsets don't require massive amounts of preload.
May I suggest backing out the bearing and checking that you have enough threads left on the steerer?

If you have, and aren't too worried about marring the knurled surface, use a pipe wrench/vise grip to screw the race down and hold it while you tighten the locknut. If you are worried, you need to find a reasonably well fitting hook wrench instead.


If you haven't, well then you'll have to find someone to extend the threads on the steerer to cure the problem.