will a 454 fit into a 78 camaro, and if it will what changes would i have to make, and what headers will fit ?

Do a search, it has been covered a few times...

yea it will fit with no modification. You will need a cowl hood for air cleaner clearence. I used summit BBC headers for 70-81 camaros
. Like said do a search I have many topics

you won't even need a cowl hood if you run a torker II #5061