Any help? Stem seems to be stuck - Seized quill stems

Yeah, its precious because I'm trying to keep the bike original. I've managed to get the top race of the headset on. Now I need to figure out a way of getting the final lock nut on there. It won't budge for the moment. Stanget that the race fits and not the nut. I'll see if I can get a bigger nut.

If you are careful with a file you can remove about 0.5mm from the top threads of the fork, ie so you can see a tiny flat appearing on the threads, this can mean the difference between it fitting really horribly, ie feeling like you are killing it with every turn...and it almost falling on, I advise you to avoid that hamfisted cunt of a mechanic again.
The method he used was bound to damage the fork, which begs the question, why did he use it at all?

If push really comes to shove and you still cannot get the lock nut on the top threads, then using the smallest available hack saw..you know the tiny ones? (like in the picture above by ocdc) they have a blade thickness of about .5mm, cut a single little cut about 4 mm down into the top of the fork, *(at the back so it's nice and neat) this will allow a little springing of the fork as you try to put on the lock nut, giving it enough movement to actually go on the fork. if after you have done it, it will tighten up without popping over the thread each time you pinch it up then all is well...if it doesn't then use a little solder to fill up the blade cut though that initial chance to get the nut on should allow it to be put on after you have filled the cut with solder.