* Firewall clearance: The 454 is substantially larger than the engines originally used in those trucks. The firewall would almost certainly need to be significantly modified or even replaced.
* Frame modifications: You might need to modify the frame to accommodate the engine's width and accessories.
* Exhaust system: Routing the exhaust would be a major challenge.
* Transmission: You'd need a transmission capable of handling the torque of a 454, and adapting it to the truck's existing drivetrain would be a complex undertaking.
* Suspension: The added weight of the 454 would likely put undue stress on the suspension, requiring upgrades.
While some people undertake incredibly ambitious engine swaps, this is one that's generally considered not worthwhile due to the extent of the modifications required. A smaller big block (like a 400 small block) or a well-modified LS-series engine would be far more practical alternatives for a 1500 Silverado.
