Hi Jeff,
Firstly, an observation! Quite a few prewar Douglas components seem to suffer from damaged threads due to the items being fully hardened. Now, threads are quite highly stressed anyway, and also suffer from stress concentrations at the roots of the threads, so the hardened threads often shatter and break away.
Now, a suggestion! Assuming you only have the thread damage, if you can get the stripped thread area of the spindles built up with TIG weld, and re-machined, the spindles should then be stronger than they originally were because the weld heat would have tempered the spindle, making it tougher and less brittle.
Regards,
Eddie