the engine block is the same there are some variations in the heads (but they will interchange) and HPOP reservoir pump. Injectors are interchangeable but OBS trucks have lower flow rates and are single shot(except ca trucks) the intake plenums are smaller on the OBS trucks & early '99 trucks.
The differences are small let us know what you want to swap specifically rather than just blanket questions and we'll be able to give you better answers. There are tons of differences and similarities and parts may physically interchange but will require other changes to support the differences.