they can be drilled for 4 1/2 bolt pattern, cut off original studs flush then drill between them for new pattern. the back side is flat and parael to front face. i have done a few of these and have not had any problems/ also, i can remove larger studs, press out the original studs install new studs back to the smaller bolt pattern. mine have been on a race car for 45 years. just food for thought
