The entire tail panel is different from 1967 to 68. Front fenders, hood, bumper, grille all different from 1967 to 68.
You can save yourself about 1000 hours of grief if you can find an MPC 1968 Bonneville to cut up.
The wheels look like Magnum 500s, but don't recall ever seeing them in a 5" bolt circle.
As far as the paint goes, Cadillac & Olds used some light yellows in the 70s and 80s that were very, very close to Mayfair Maize.
Dupli-Color also made a light yellow in their small aerosol 'Import' line. Am thinking they quit making the small cans, though.
1992 Buick Roadmaster Canyon Yellow is also pretty close.
posted at 3:36p EST