Nope. No such thing as SBP 11" brakes, they were all 10". Only way they could be 11" brakes is if that's a BBP 7 1/4. They wouldn't have been there stock in that case, but they fit.
With a 7 1/4 you're pretty much screwed too. The SBP and later BBP 7 1/4's are different, you can't swap BBP 7 1/4 axles into a SBP 7 1/4". You'd have to have the SBP axles drilled for BBP, and then do the same with the SBP brakes. Or swap out the rear axle entirely.
