I have a 67 Impala SS. For a while I ran 295/65R15 MT drag radials on a 9" wide rim. The specs for those are: 11.8" wide & 30.1" tall. Those tires don't have a good reputation in the rain and I wanted to go on some longer trips. So I switched to 265/70R15 BF Goodrich street tires on the same 9" rims. They are: 10.7"wide & 29.7" tall. Still fill up the wheel well pretty well and no rain worries.
The 285/70R15's you want are 11.5" wide & 30.8" tall. So the width will work, but because the front of the wheel opening turns back, I would worry about the big diameter hitting the wheel opening.
When I had the 30.1" dia MT's that area was too close for comfort.
AND, I also took out the spring pocket bump & replaced it with a flat piece. That gave me an extra 3/4" room on each side. I also rolled the fender lips.