Size of rear wheels ?

I was wondering what size wheels I could put on the rear of my 71 Chevelle without any modification to the stock rear end 20 x 8.5/ 20 x 9 or 20 x 9.5 I was going with 18 x 8.5 in the front and 20 x 8.5 in the rear the car will be lowered 2'' in the rear.