Looks like an easy install to me. Do you want to use this in place of the start function of the ignition key or as an auxiliary start function?
If this will replace the key function, this is the way I would do it:
1.Locate the wire from ignition switch that goes to the starter solenoid and remove it.
2. connect the wire to the new switch.
3. run a 12 volt feed wire to the new switch from the ignition switch, making sure that the source is keyed(meaning it only has 12 volts when key is on)
4. mount the new switch where it will not be bumped. This is also a cheap "anti theft devise" if concealed in a non-visable location, such as up under the dash,under seat, etc, but might be a pain in the butt after awhile.
One thing to keep in mind is that the switch should still be wired in with the neutral safety switch.Nobody wants to see a pic of your car halfway through the back garage wall
I wired mine in the other day. Take the purple wire from the column that feeds the starter solenoid and cut it. Strip both ends and attach them together on one side of the switch. Get a 12 volt source with the key on and attach it to the other side of the switch.
This setup will allow you to start the car with the key on using the push-button or use the key to start the car if you get lazy and don't want to use the push-button.
Some push buttons come with a light. I'm getting another set up open contacts for my switch and a 12 volt relay to get my push-button's light to come on when the switch it turned on, and then go out when I push the button. If you don't have access to 2 open sets of contacts, then 2 relays can be used.