Read the V6 to V8 swap sticky in the top section of this forum.
Understand that a carbureted SBC is only an emissions-legal swap in an '88 chassis per Federal law if equipped like an '88 Monte Carlo (i.e., 305 q-jet).
The basics are covered in the sticky. Anything more specific would require more specifics from you (engine size, transmission type, intended use, budget, etc.).