If you really, really don't want to scrap it, then you will have spend a really, really long and tedious time with with a tiny jewelers file to clean up the threads well enough to get a FW started on it.
The real key to this will be carefully threading on the freewheel so that it catches the original threads and not the newer "threads" the cross-threading created. A FW ittself is pretty unwieldy for this, and you can't really see in there to see what is happening. So, instead do it with an old BB lockring. Same size and threads, and they are small enough that you can see and feel exactly what is happening.
File is up as best as you can. Then carefully chase on the BB ring a few times and then take it off. Then carefully thread on the FW. This is a doable task if you have the desire to save the hub.
jim
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