For the 87-90 pickups with the 2.6l engine and 5-speed trans, the parts list I have shows P/N MD703782 for the input shaft assembly and MD725209 for the input bearing. It doesn't mention stepped or non-stepped. This Japanese website sells individual shafts (at a breathtaking price.)

https://www.megazip.net/zapchasti-dl...drive-MD703782

Others looked like you have to by minimum quantities. Your best be may be to find a used shaft or trans. How exactly did yours go bad?