* Engine Mounts: The 350 and 454 have different engine mount locations. You'll likely need new motor mounts designed for a 350 in a 1994 Cheyenne, or potentially fabricate custom mounts.
* Transmission: The transmission compatibility depends on what transmission the 454 had (likely a TH400 or a 4L80E). A 350 might use a different transmission (TH350, 700R4, 4L60E are possibilities). If the transmissions are incompatible, you'll need to swap the transmission as well, which is a major undertaking. This also impacts the driveshaft, possibly requiring modification or replacement.
* Wiring Harness: The wiring harness for the 454 likely won't be compatible with a 350. You'll either need to modify the existing harness (challenging and not recommended for beginners), or source a 350 harness that's compatible with your year truck.
* Exhaust System: The exhaust manifolds and pipes from the 454 won't fit a 350. You'll need a new exhaust system.
* Computer/ECU: The engine control unit (ECU) will need to be compatible with the 350. This might require a complete ECM swap.
* Cooling System: You might need to adjust the radiator and hoses to match the 350's cooling requirements. The 454 is a significantly larger engine, so the cooling system designed for it might be overkill for a 350.
* Other potential issues: There could be other minor compatibility issues that you'll uncover during the swap, such as differences in accessories (alternator, power steering pump, etc.)
In short, while the swap is possible, it's a significant project requiring mechanical expertise and potentially a considerable amount of time and money. It's far more complex than simply removing one engine and bolting in another. You should have a good understanding of automotive mechanics or consult with a professional mechanic before attempting this.
