Has anyone ever switched the body off a 97 step side 2wd on to a 98 straight bed 4x4? If so what problems might I come across?

 

Welcome to the forum

If you are doing the WHOLE body, including rad support then should be no issues, assuming both are regular cab or both are extended cab
Rad support was changed between 1997 and 1998 model years, so 1997 front end parts won't bolt to 1998 rad support

The step side rear bumper is narrower so also needs to be moved over