I'm pretty sure I've mentioned previously that I didn't like the aesthetic of the real models, something about Space Marines in armour donning a second suit of armour just to tout big guns didn't really do it for me. These are the Mechanicum Kataphron Destroyers with marine heads and backpacks. It was a super simple conversion.
They're mounted onto 50mm bases (which I'm pretty sure is what marine destroyers come with) so you can see they aren't too dissimilar is size for gaming - a little shorter, but wider.
Eventually I need to figure out a way to model their secondary weapons (either missile launchers or hurricane bolters), but that'll be an addition for another time.
I'm sure they'll die horribly and do absolutely nothing in their first game, such is the life of any new shiny model ;)