Transformers: Beast Wars NEO UNIVERSE Decepticon Dropshot customized as the MAXIMAL Commander Big Convoy, here with original counterpart. For mode decided on a type of tank with both functions as Assault Gun (trunk) and Siege Weapon (tusks)
Is he a headmast?! I think I see Hardheads cockpit and that is definitely Titans Returns Voyeger Optimus Prime's head.
Cool! You weren't that far off, especially with the double cannons on each shoulder. Here's a pic from the tfwiki page if you're interested: