what mods to fit 26x12.5x15 et streets?

I already have 275/5015 nitto drag radials on there, but want to step up to the et streets. dont know if i should get the 11.5 or 12.5 width. I dont mind massaging in the steel frame panel on the inside of the frame. I already have the bumpstop removed, will I need to pound in that frame? anything else needs to be moved/clearanced?
chris

this is on a 10" rim btw

Is the 26x12.5-15 ET Street "new"? I went to the M/T ET STREET (http://www.mickeythompsontires.com/strip_et_street.html) listing to see what the section width was, and they only list a 10.5 and an 11.5.

What is the section width on the 26x12.5? What is the backspace on your 15x10 wheels?

I have a 4gen rear in my Iroc, and the rims fit both cars the same. I have 7.5" backspace rims. I thought I saw them before? maybe Im wrong. ohwell, Im goin w/the 11.5 so they will fit both cars w/o haveing to mess w/them too much.

11.5 is the proper call with 7.5 BS.