Need help with size, thinking 18's on a 68 dart

I have been reading on this site for some time and could now use some help. Four the past four years I have been getting my wife's 68 dart 270 back to road worthy. I'm trying to get it back to her for christmas for a suprise. It has factory V-8 k frame, 76 dart front suspension and brakes, factory 8.75 rear with BBP axles and drum brakes, leaf springs are in the stock location. Trying to get some 18 inch wheels and tries, but not sure of what back spacing to get and would like to run same size tire front and rear. Any help would be great. I'm ready to buy wheels and tires right know. She likes grey and black 5 spoke design. Anybody with pictures would help also. I have put a ton of time into this car and want it to look as good as she thinks it can in her dreams. She has not driven this car for almost ten years.