There is at least 2 different ignition switches for '70's pks.
1. Points ignition version
2. Electronic ignition-no points, odd looking coil version.
This will determine which switch you need.
There is quite a bit of interchange of common parts like this between the garden tractors, so if you have the switch you need to replace and take it to a "good" auto parts store they can probably match it to the right replacement switch.