* Engine Size and Type: If both trucks have the same engine (e.g., both 5.7L V8s, or both 4.3L V6s), the chances of a relatively straightforward swap are higher. Different engine types (e.g., a 5.7L swapping for a 4.3L) will require more work.
* Engine Mounts: Engine mounts changed over the years, so the engine mounts from the 89 might not perfectly align with the 94's frame. Fabrication or modification of mounts may be necessary.
* Wiring Harness and Computer: The engine control systems (ECM/PCM) changed significantly between 89 and 94. The wiring harness from the 89 engine might not be compatible with the 94's system. You'll likely need to adapt the wiring harness or use a stand-alone engine management system.
* Transmission: The transmission must also be compatible. Ensure that the transmission from the 89 truck is the same as, or compatible with, the transmission mount points on the 94 truck.
In short, while the general architecture is similar, you'll need to carefully compare specific engine and transmission details between the two trucks. Consulting a repair manual for both the 89 and 94 models would be essential before undertaking this swap. Expect to encounter some challenges and modifications. It might be a much simpler process to find a used engine from a 94 Sierra.
