Yeah, a push button should buy you some time. But you should still hunt down the real problem as soon as you get a chance.
The actual ignition switch is behind the dash, on top of the column. It is operated by a rod, that is moved by the ignition actuator, which is driven by a toothed gear, that is turned by the cylinder. If any of that goes bad it can cause the actual switch to not move far enough to reach the "start" position. If that is happening the most likely culprit is the pot metal ignition actuator, which is prone to fail as these trucks get older.
Sometimes you can buy more time by adjusting the switch on top of the column. On my 90 I first adjusted the switch, then replaced the switch, but finally had to replace the actuator to really fix it. IIrc that actuator also unlocks the shifter & steering, so it is likely that the pushbutton bypass is only a temporary fix.
Sixlitre gives a quick test/bypass if the actuator is starting to fail here:
Reach down lower on the column and find a steel rod running down the column. Using a pick tool or bent needle nose pliers, grab the steel rod and pull down on it with yo' left hand (while you have the key turned all the way on, with yo' right hand).
Bet you get a vrooom noise then !
If you determine that the actuator is failing, here is a good thread with more info added in throughout. I followed these instructions to replace it on my 90, but didn't have to drop the column as described.
The pics appear to be gone, but you can find them here:
Click on any pic for a larger version.