If the owner is going to show his/her 69 mach1 in the concours trailered/driven class, then yes, they will get a deduction for magnum 500's.
But its personal preference IMO. If the owner would rather install the magnums because he/she likes the looks better than the Styled Steel wheels and get the up to the 5 point deduction, then that's his/her choice.
I have an aftermarket am/fm radio in my 69 mach1 cause we enjoy driving our mach1 and we get dinged the points everytime in concours driven( have since made it into the conservator class).
I'm a certified judge and in Orlando a few weeks back we counted off for magnums on a 69 mach1.