That's a 27" tall tire. Going to be pretty hard to run that in the front.
I'd suggest a 255/40/18. That's a 26" tall tire, which is just about perfect. GmachineDartGT runs 255/40/18's all the way around on his '71 Dart.
With a Valiant a 275 in the back with just the spring offset will have to be spaced just about perfect if its going to work, the 255 is a much safer bet.