Challenges:
* Space: The 454 BBC is a large engine, and the El Camino's engine bay isn't designed for it. You'll likely need to modify the firewall, inner fenders, and possibly the front suspension to make it fit.
* Cooling: The BBC generates a lot of heat, so you'll need to ensure adequate cooling with a larger radiator, electric fans, and possibly a different water pump.
* Exhaust: The exhaust system will need to be modified to accommodate the larger engine.
* Transmission: The stock transmission may not be able to handle the power of a 454 BBC. You might need a stronger transmission, like a TH400 or a 700R4.
* Driveshaft: The driveshaft may need to be lengthened or shortened to accommodate the new engine and transmission.
What to Consider:
* Experience: Do you have the mechanical skills and knowledge to make these modifications? This is a significant project that requires expertise.
* Cost: Modifying the El Camino to fit a 454 BBC will be expensive. You'll need to purchase the engine, transmission, parts, and possibly hire a mechanic to help with the installation.
* Performance Goals: Do you really need the power of a 454 BBC? A smaller big block, like a 400, might be a better option for your needs.
Alternatives:
* Small Block Chevy: A 350 SBC (Small Block Chevy) will fit more easily in the El Camino's engine bay and still offer good performance.
* LS Swap: Modern LS engines are powerful, fuel-efficient, and relatively easy to install in classic cars.
Conclusion:
It's possible to fit a 454 BBC in a 1981 El Camino, but it will be a challenging project. You need to carefully consider the challenges, costs, and alternatives before embarking on such a project. If you're not experienced with engine swaps, it's best to consult with a professional mechanic.