64 front brake drum removal

[truckeroy]

I know somewhere on this site this question has been answered, but I can't find it. I've got a 64 1/2t with drum brakes. I removed the rear drums with much effort, using a homemade puller and 1/2 a days work. I want to look at the front brakes and i am having the same problem with the front drums. My manuals don't say anything about the drums being riveted on, but these drums have 3 round head rivets on them. Does this indicate the drum is riveted on and need to be drilled out, or are these just buttons on the surface of the drum? Thanks, Roy