67 Valiant tire and wheel fitment

I can't answer for the front, but for the rear, unless you use offset shackles, you won't get a 275 in there. As far as using the B body rear end and the wheels you're looking at, I have only one question...
How do you feel about radiusing the rear quarters?
I have a 76 Duster 8.25 rear in my 69 Valiant and am running 255/60R15s on 8" wide wheels with 4.5" BS. It's close to the spring and the wheel well lips.