Thanks all!!! Would have ruined these shock mounts without all your help!
Update: decided to start with the thread chasing file. Practiced for 15 minutes on a old 10x1.25 bolt that I purposely mashed the threads on, then I took my time filing the shock mount (using a circular motion, credit BenelliSEI), finally was able to partially thread on a nut, so oiled everything and ran the hex die down the threads. When I thread on a nut, the threads feel like the other shock mount.