If your axle is centered perfectly, you can run the 285 wide tire on the '69 if you are willing to cut the outer fender lip down, or roll it flat. Might also need to move your exhaust tips, if they are next to the back of the tire.
Wheel offsets are going to have to be perfect, too.
I had a pair of 285/35-19 on my previous car. Stock wheel tubs, stock axle, 10.0 wheel with 5.5" backspace, rolled outer fenders, hammered a little on the inner wheel housing. But, it worked.
Tony