Hey man
I'm glad I'm not the only one who made some Ogryn Kataphrons!
I did mine slightly differently, I used WFB Ogres as a base, then mounted the weapon into the model's right shoulder. I then green stuffed re-breathers over their faces, added smoke stacks to their backs.
Built myself some metallic monstrosities!
Fluffwise my army is based around a Mago's trying to "reboot" the original Mechanicum. To break away from Mar's Control and be free to develop new technology to combat the enemies of the machine god. (Renegade but not Heretical)
So I imagine he needed Kataphrons, had no Kataphrons but had some Ogryns lying around and put two and two together. Literally.
My army is also dragging around Skaven Cannon Fodder.