I'm in the "planning" stages of using a E.F.G.F. M61A5 MBT "Semovente" Phantom Element as the basis for my Space Marine superheavy. It looks much more like something a Space Marine chapter would field than a Baneblade would.
I was planning on using the Vulcan Mega Bolters as the main gun, but after seeing how teeny-tiny they actually are I'm going to have to reconsider my options - or at least reconsider putting on the turret.
In any event, I'm intent on putting hurricane bolter sponsons on each side as defensive (anti-personnel) weapons.
Or, you can do what this guy (morfangdakka) did: