73 dart sport rear wheel and tire what will fit

I have a 73 dart sport at the moment it has 7 1/4 rear im gonna put ford explorer 8.8 disc brake rearend,im gonna narrow the long side to match the short side springs in stock location.Iwanna run 275/60/15 in back.iI found 2 sets one set is 15x8 4 1/2 back spacing and the other is 15x10 with 5 1/2 back spacing witch will fit better with the 275/60/15 tires