Why swap to the bigger bolt pattern? Uh, because there's basically nothing other than stock designs or Cragars for the SBP? That's not a lot of options. Some of us don't like either of those. But that's a matter of opinion. That doesn't even get into running something other than stock brakes, and it certainly doesn't address tire selection. The KH's and 10" drums do a decent job for stopping especially with the kind of grip (or lack thereof) that you get out of BFG T/A's, but of course you can do better. And replacement components for the SBP brakes are not always easy to find when it comes time to replace rotors, drums, etc. At the moment pretty much everything is available, but there have been long droughts when you couldn't get the parts you need to rebuild those brakes new. Meanwhile, BBP brake parts are relatively cheap and easy to find and you have a huge selection of various rim sizes and designs to choose from.
As for that tire/wheel combo, in the back you'll have about 1 mile of extra clearance. Ok, not a mile but it might as well be. 235's in a space that will hold 275's. 255's would be easy with those rims.
In the front you'll be further out to the fenders than you need to be, but it should clear just with the narrower track width of the SBP disks. Shouldn't have any problems.
