* Wiring Harness and Computer: This is the biggest hurdle. The 1995 and 1999 systems will be different. You'll likely need to either use the 1999 harness and computer with the 1995 engine (which might require some rewiring depending on minor differences), or adapt the 1995 harness to the 1999 system (more complex and potentially risky). A professional reprogramming of the computer may be necessary.
* Sensors: While many sensors are the same, some might have different connectors or slight variations. You might need to swap sensors or adapt connectors.
* Exhaust Manifold and other parts: The exhaust manifold might need to be swapped, or at least adapted depending on the minor differences in the engine between the years. Other minor components like brackets may also need to be swapped.
* Transmission Compatibility: Ensure the transmission from the 1995 engine is compatible with the 1999 Blazer's transmission. This is less likely to be a major issue, but it's something to verify.
In short, it's *possible*, but it's not a simple drop-in replacement. It'll require some mechanical and electrical expertise, and likely some parts swapping. If you're not comfortable with automotive electrical systems and engine swaps, it's best to have a qualified mechanic handle this. The cost of labor could easily exceed the value of the engine swap.
