[jdurant]

I just looked and couldn't find a 285/70. Either way, that would be a really tall tire. When I was looking for tires before, even places that listed 295s--didn't really have them, they were on backorder or discontinued. You might get lucky and find somebody with some old stock.
And any trim ring that will fit your stock 8"s will also fit the 10"s. The lip is exactly the same.

For those that don't know, this is how you read a tire size.
295/50/15
295-measurement of how wide the tire is in mm.
50-is the height of the sidewall, but an aspect ratio--in this case 50% of 295=147.5mm tall
15-is obviously the diameter of the wheel.

so a 285/70 would be considerably taller than a 275/60--which in my opinion is about as tall as you want to go.