Mr. Harwood,
i just checked my invoice and it is dated 9/21/16, it is strange that Diamondback says that they no longer have that size available. I must confess that the reason I went the Diamondback route for my car was due to your terrible experience that you had with your 90 Limited with new bias plies while you were traveling to the Buick National meet. That story convinced me to go the Radial route with Diamondback. I have 2 other sets of Diamondbacks on other cars I have, but on the Buick I was going to go bias plies.
When I had the tires mounted, my technician was amazed that none of them took more than an ounce of weight, and that they were round! When I asked why he told me that the other popular manufacturer's tires took a significant amount of weight and they weren't always round.
Your Cadillac looks great with the tires you selected, I hope they perform well for you.
Jack