Will the tires fit on stock 15x7 '87 GN wheels? Yes.
But...
Those tires really need a 8" rim or so. Mounting them on the 7" rims will wear out the centers of the tires more quickly. I've seen it happen.
So, you can either just do it and put up with the wear issues, get some wider rims, or have the GN rims widened. Truedesign Wheel in Colorado is one service that does this, and they do a very nice job. GBodyParts is doing this as well.
http://www.gbodyparts.com/product_in...cddf6137414840