I have the SN95 spindles that came with the M2300K Cobra brake kit. I dont know of a Cobra R rim with 9.5" width (unless we are not talking genuine Ford, which are 9").
Look at my sig (and website), there is a "wheels" page, and LOTS of Mustangs with Cobra R rims with 275-40-17's at the open track events.
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Darius Rudis
Roadracer: Home built t-arm/panhard suspension powered by an S-trimmed motor :-)
My Mustang Page