Going with wide whites does limit your options. 

I don't know if it will help, but the 55-56 T-bird wheels are 15 x 5/w 6.70/15 tires. I would think full-size, with the possible exception of wagons, use the same size wheels and tires. Pretty much all of the cars had tall, skinny tires in the 50s. 205/75r15 is a common replacement for the 6.70/15. 

(From the photos it appears that all 5 beauty rings are in excellent new condition, he was asking $295 plus $49.51 shipping then there was a tax fee when I was going to purchase of some $40 which put the total almost at $400 which I felt was too much as it was something like $380 which made each trim ring $76.)
$49.51 shipping
$40.00 Tax fee
Sorry, but this deal does not smell right to me.
What do you know about the seller?.

Correct, there are two listed tire sizes for the passenger cars for 56, the 6.70-15 and the 7.10-15.  The 7.10-15 I know was used on wagons and cars equipped with AC but I think I saw in one of my books that the 7.10 was also used on optional Thunderbird Y8 equipped passenger cars with automatic transmission.  Tires I currently have are 205/75R15, the old tires that was on the car I dont have a good enough photo of them to see the size but the spare tire in the truck which is a old Gillette tire pre 1980 tire is a F78-15 tire.

1956 Ford Fairlane Town Sedan - 292 Y8 - Ford-O-Matic - 155,000 mi