78 caprice big block headers ?

I am hoping someone can help I am putting a 396 in this 78 caprice. I know they don't come with big blocks. So my question is what car that came with a big block would be best to buy the headers for and install with the least amount of mods. The crossmember has already been modified. The car has already had a big block in it but the previous owner didn't know what headers was used. And I bought it as a roller.