I just went through this.
The steering lock has a metal shaft with flanges(?) which mesh with the *plastic* ignition switch. When I removed the cowl from the column, I discovered that the plastic had, for lack of a better term, become wallowed out.
This meant that the key wasn't turning the switch.
You should be able to touch the lower ( white or yellow, I think) wire from you relay to the lowest connection on the fuse box and the starter should turn. In fact you can start the vehicle that way if you get tired of pushing. John Twist has a video describing the process in detail.
You should also be able to hotwire the car using a screwdriver on the back side of the ignition switch. I did it using my patented fumbling around technique.
If you can't get the starter to turn using the above, it may not be the switch, but rather a wiring issue between the switch and relay.
If it is the switch, I suggest you replace the '74 ignition switch and steering lock with an assembly for a 70-72. Not only are the mating surfaces *metal*, but it's about half the price of the same thing for a '74.
If you go that route, the purple wire and the slate wire will not be used. Purple is seatbelt, I believe and slate is for the anti-running on valve. If all of your emission control devices are intact and required, you may not want to go with this solution.
It worked for me.
Good luck.