275 is pretty much the max on the stock 8" rim. My tire guys bitched the entire time they put some on my stockers because it took forever. I wouldn't go 285.
Now 03/04s are 9" rims and will take up to a 315 nitto nicely.
I wouldn't run a 275 on an 8" rim on the front. You'll have too much "tracking" of the grooves/ruts in the road, not to mention sidewall flex in turns.