The 66 Plymouth front splash shields are definitely different than for the 65s. The rears might be the same; the ones I pulled off the 66 I parted out were too rotted to even mess with.
I'd be interested in purchasing a set of splash plates (at least one frt and one rear - would purchase in pairs if needed) from a 66 Dodge, 66 Plym, 63-65 dodge and 63-65 Plym to confirm.