I am creating a legal size form with a letter and a two-sideds postcard at the bottom.  The letter will change but the postcard design will stay the same.  I got it to work by creating a detail A with the letter and front of the postcard at the bottom to fit the page size of 14 inches, then created a detail B after that with the back for the postcard at the bottom to fit the page size.  Would like to know if this is the best practice to use when creating such form?  Any help would be appreciated, I'm a beginner.  Thanks