There are 2 tanks for CX500, the original '78 tank became the Deluxe tank in 79 through 198x. In '79 they introduced the Custom. Mounting may have changed again in 1982. These are for U.S. models and other areas may have other differences.
Both early styles of CX500 tank have a single bolt in the back but the front mounts are different. The Deluxe front mounts are rubber pucks on posts. The Custom tank uses bolts farther forward.
I can't help you with info on 400F. Sorry. You'll have to specify if your CX tank has knee cutouts (Deluxe) or is teardrop-shaped (Custom).