With Guard, it is the same with normal, vanilla Marines for their weapon options: One heavy, one special. Chaos and SoB have the option to ignore the heavy and get a second special, but, thats those armies(for now. Chaos' been shafted give time for that, but, they got oh so much more in return)
Guard HQs can take mixed weapons like that, however, it makes them a really expensive fire magnet. Best to have them hide.
I am curious to see how this list will survive.