Ignition Failure

I have a 1985 Jeep Grand Wagoneer (150,000 miles).
I went to work one morning and the car started just fine. On the way to work I could hear sounds like "leaves in the air duct/vent" on the right side.
I made a pit stop for 15 minutes; I started the car again, only this time, the engine started to race at a high rate and I could not disengage it, nor could I turn the engine off (the ignition key would just turn freely, not engaging). The car runned at a high speed for about 10 minutes at the end of which, the car started to smoke a lot and shut down and would not start again. The main problem is that the Key will not engage the ignition, the key turns back and forth and does nothing.
Since then, I have replaced the starter, the selenoid switch, the ignition barrell and the ignition switch.
What am I doing wrong or not checking?
Please help.