I wanted to pull my 454 big block out of my 1975 suburban and put it in my 1981 El Camino, will it fit ?

In California cars 1975 and older are smog exempt.

81 chevy had limited emissions Basically a cat, O2 sensor and a sort of computer controlled carb. The year of the engine plays no part in emissions, the year of the vehicle does. I have a 41 Ford running a destroked 427 It is exempt from emission testing That being said, I see a few issues with your plan. After 1970 the car makers lowered the compression ratios to meet emission reg, So the 75 454 is a nice boat anchor unless you want to a bucket of money into it. But it will fit. Now you will still have to change the exhaust system, and a bunch of other stuff. You can dial in the tail pipe emissions to 81 spec's by hooking up a scan tool and adjusting the carb by watching the O2 cross counts

Thanks for all of your answers, and thoughts to my question, I'm really leaning towards an LS 5.3 vortec, way less of the headache.