Hang in there, Scott. What you've stumbled into is just another of the mysterious 73 TX650 documentation foul-ups.
70-71 front drum brake uses a rotary stop switch, activated by a post on the lever.
72-73 hydraulic front brake uses a similar (306 variant) rotary stop switch, also activated by a post on the lever.
1974 TX650A dropped that, uses a pressure actuated switch.
Here's some pics that show all I could find concerning the 72-73 front stop switches:
This 70-73 parts snippet shows part #43, two versions, 256 for 70-71, 306 for 72-73.
This manual excerpt is the only one that has any mention of that 72-73 stop switch:
This manual snippet shows the rotary stop switch, just above and pointed to by the "throttle adjuster" arrow.
This 72-73 manual snippet shows the disc brake system.
There's no mention of the mechanical rotary stop switch.
This 1974 TX650 manual snippet shows the disc brake system.
Notice that the stop switch is now a pressure switch, mounted on the manifold.
Goofy stuff, huh. Clear as mud?