yea man, massive sidewall. Personally id only ever fit a 205 to a 13 inch rim if it was 9 inches wide :p
You could easily get 175/50's or even 60's on them without a sweat. A 175 on a 7 wont have a lot of stretch on it either.
dooo ittt
edit: heres a 175/60 on a 7 and note the lack of stretch. The sidewall is level with the rim face instead of bubbling over it (ewww).
and with the valley in the watanabes being close to the rim edge there shouldnt be any problems what so ever with getting them on
stretch on a 7 would be a 155 or 165.