Ignition coils generate heat, with some more than others. Pamcopete highly recommends mounting the coil so that the heat is transferred to the frame tube. He has a method that uses grounding lugs that are bought at Home Depot electrical section. Look in the "Tech" section, and in the "Shops" section on this site for "Pamco Ignition". Also "search" for Pamco ignition.............there are many posts on this topic.
For another method, check out this pic of my bike which has an Accel coil (yellow in the pic) that I mounted to the horn mounting bracket which is rubber mounted. This works for me because this coil does not generate much heat.
You could PM Pamcopete with the coil you bought, and he will recommend a mounting method.