255x50x15 on Skylark GS rims

Hopefully Im jn the right area of the forum here...
The Buick Skylark GS Stage 1 wheels are I gather 15x7"
Is this the OEM factory sizing.
I have an idea mine has possibly haf replacement copy wheels fitted...
The wheels look similar to Magnum 500 I think theyre called, Im definitely no expert on USA factory sport or rally wheels so your input will be appreciated.
Mine are fitted with 255x60x15 BF Goodrich radial TAs
Is this the widest I can go on 7"
rims with safety?
If in fact mine are 7", without removing a tyre/tire I cant verify.

 

This is probably the best pic.
Here Im setting up some 9inch rims with ET Streets for the drags

 

Had a look at one of my wheels today and its a 7"er

 

I have 255 60 15's on factory style steel wheels that are 15x7
Ive seen guys go 275 on 7" wheel, sidewall balloons out more.

 

Whats the story on the Magnum500 wheels?
Were they OEM on Buick GS Stage 1
an option maybe?
Looking through old magazines theres ads for just the wheels and
They appear on both Ford and GM vehicles as well as Mopars...
Whats the story with them?

 

Buick never used Magnum 500 wheels. The Buick wheels are a different design only used by Buick.

 

Ok thanks Mike, to me they look the same or similar.
Could you or someone possibly post pics and show the differences?