Hi A.J.
I've read that the chassis color matching the body wasn't uncommon on full custom-bodied cars. Packard would finish the Custom and Deluxe Series cars to customer specification if so ordered. Is it possible your Dietrich was built for the car shows and in order to heighten it's appeal, they finished the chassis to match? You need to submit this question of chassis color matching or complimenting the body color to those more knowledgeable on the CCCA Forum. Definitely there are some members there who can enlarge on this Classic Era practice.
Steve
Just a small note.... Packard did offer the option of having a chassis painted any color. In my particular case, I have a 1933 1001 Eight convertible coupe (that is the small Packard in that era) which apparently was one of the showroom cars in the Packard Motor Company distributor in New York... and even though it was the smaller Eight, the car was fitted with most options available, including having the chassis in body color, which was silver, so the chassis was also done in silver. I guess it was an "In" thing, on fancier cars and my little car got it because of being a showroom car.
I don't see why not your Custom built car could have been treated the same way. After all, in an era of early streamlining and integrating more the car's components (even the two tone cars were becomming a bit old fashioned), a monotone car with a similarly painted chassis would surely be striking. My two cents.
Your car is stunning, and it will be anyway you do it! But as you can see, and I am sorry if I seem a bit intense, I certainly can't hide my liking of a monotone car with the copper accents on trim.
victor