Wheel Offset Question
 

I have a 78 sc that just got converted to a widebody using 930 parts. I bought cup wheels but don't know what spacers to buy to make them fit right. They are 7 inches wide up front and 8's in the rear. The front is 52m and the rear 55. I think a 3 inch spacer will do it for the rear but I'm not sure. Any help would be appreciated