Giant sponsons for a giant tank.
Repurposed Earthshaker cannon for frontal attacks. The range is lowered if only as the Earthshakers cannot angle upwards enough.
Beyond that, Twin Lascannons and Im not sure what Ill have on the rear of the sponson. But I know on top I want short, squat battle cannons turrets (so the main turret doesn't hit them) and a Heavy bolter turret or two somewhere.