Here's what I did.
1. Remove tailpiece and drill out the four marked holes ~5/8"
2. Take a piece of 1/4" aluminum plate about 8" square and drill to match
3. Make bushings to hold the plate about 1/2" above the tailpiece
4. Reinstall the tailpiece and bolt the plate in place
5. Now you have a solid platform to bolt a home made or aftermarket luggage rack to!
Good luck! If you'd like pictures send me a note
Ray