i know its a huge change,but we got an 84 sport coupe[had a 2.8 v6] and we're getting a 454 attached to a turbo400 for almost nothing,will it fit in my camaro..?

 

yes. it will require some suspension changes.
1984 Big Block 454 Camaro Z28 Burnout - YouTube

 

you can go bigger too. if you go with a tall deck then you'll need to change your hood.

Cooling, mounting and suspension will all need to be modified

I hope you just aren't taking a junk engine (one that has not been paid for by you to be rebuilt ) and tossing it in thinking you are AOK then you may wish to re-think the labor

you're also going to need to replace the rear end

 

Camaro Tech: Chevy Camaro Big Block Engine Swap

Don’t neglect the cooling, for every HP you make you have to bleed off 1 HP of heat. The 2.8 is around 145 HP and its cooling system is sized for it.

 

Can't over-emphasize the above two posts. If its a mid 80's big block that has miles on it...don't expect it to act like a performance motor. Some of those mid to late 80's 454's put out around 270HP....not worth a high dollar and very very labor intensive swap. If you were to rebuild both the motor and trans with some mild performance parts and know its not a time bomb, then it would most likely be worth it. Keep in mind a lot of things change as the 3rd gen never had a big block option. Items like mounts, crossmembers, manifolds/headers that fit are going to be tough to come across. The cooling system will need upgraded, and things like driveshafts and torque arms will need to be fit to that drivetrain.