Before 1969 the lock cylinder and ignition switch were one part and mounted in the instrument panel. You removed the lock cylinder from the unit with the ignition key and by inserting the end of a paper clip into a small hole in the face of the lock cylinder. The ignition switch was part of this assembly but was hidden behind the instrument panel.
1969 marked the first year for the function locking steering column. Now the ignition lock cylinder and the ignition switch were separated. The lock cylinder was placed in the steering column head. The ignition switch was mounted down under the dash, on top of the steering column jacket. Also the switch tucked up into the brake support bracket and was quite inaccessable unless you dropped the steering column down from the instrument panel. (Difficult for a thief to hot wire; time consuming to service.)
Lock cylinders can be interchanged on all Saginaw columns made between 1969 and early 1979. Sometime in 1979 the lock cylinder retention method was changed. The first 10 years the lock cylinder had a metal wedge that snapped into the column housing head. Sometime in 1979 a seperate cross bolt was introduced to hold the cylinder in place. This made the ignition lock cylinder much more difficult for a thief to "slam" the cylinder out of the steering column. The 1979+ lock cylinders will not interchange back to the earlier columns.
There was one design ignition switch for standard (non-adjustable) steering columns and another switch for all adjustable (tilt as well as T&T) steering columns. Both switches operate by means of a rod the pushes and pulls on the switch through a linkage system connected to the lock cylinder. Because the linkage systems are different between standard and adjustable steering columns, the switches operate in opposite directions from each other. This also causes the electrical blades between the two ignition switches to be mirror images of each other.
Switches that are used with adjustable columns operate on a pull basis. (When you rotate your ignition key clockwise from ACC you are pulling the rod and the mechanism inside the switch up toward the driver: ACC, OFF-LOCK, OFF, RUN, START)
Standard columns operate on a push basis. (When you rotate your ignition key clockwise from ACC you are pushing the rod and the mechanism inside the switch down toward the engine.)
The vehicle wiring harness was the same regardless of the type of steering column. You mearly needed to twist the vehicle wiring harness connectors 180 degrees to make them snap into one or the other of the ignition switches.