Yeah I thought you'd be pretty close to the limit there with a 17x8" and that backspace. Normally I'd say that a tubular UCA would solve the issue, but you're SBP so that doesn't leave you much in the way of options for tubular UCA's.
You can just run a bit less backspace than 5.25" though. 255's are the best you'll do up front on 17's, so given how much track width is gained by going BBP I'd say you can probably go with a 17x8 with a 5" backspace and still run the 255/45/17 if you stay SBP. That should gain enough space to clear the UCA and just using some math between the BBP and SBP tracks you should still be inside of the 275/35/18's I run on my Duster on the fender side as well.