Tater, you and I are now qualified Winchester gunsmiths. Before I logged on I had a eureka moment, light bulb over my head, and a dazzling mental sunrise that resulted in demystification of the 121 bolt.
After trying various gentle approaches to disassemble the bolt I clamped the striker head and turned the bolt body clockwise. Sure enough, threads appeared. Turned the bolt body counter clockwise while pulling and compressing the striker spring and the threads began to disappear into the striker head. The more turns the less spring compression and turning effort. The striker rod and spring soon popped out, the bolt had been disassembled, and blue birds sang.
Thanks for your help and concern. We are now experts and, contrary to implication of the TV commercial, Holiday Inn Express was not needed.