This will sound weird, but it can be a damaged rack & sector. The Ignition rod is activated by a sector gear at the end of where the key cylinder hooks in and enguages a rack that has the rod attatched to it. Lay your hand on the ignition switch on top the column, turn the key and see if you can feel movement in the switch. If you dont, then disassembly of the upper end of the column will access the rack & sector part. If you feel movement, then I'd go after the switch. The rack is made from a " cheezy" pot metal material and can crack & break. The sector is plastic. see link below, part # 24
http://www.lmctruck.com/icatalog/cc/full.aspx?Page=136