Thanks for such quick replies guys. Super helpful. You guys really know your stuff!
Did a little more research building on what I learned from you guys and it looks like the plasma cannon is a "Heavy Plasma Gun" that the old Rogue Trader rules for Ork Dreadnaughts allowed. Saw it on an old post on a neat custom Rogue Trader Dreadnaught build. (Will link)
Looks like he has, 1x Las Cannon, 1x Bent Power Claw Arm, and 1x Heavy Plasma Cannon.
Do either of y'all know what that horizontal crane-like grabber is called?
Thanks again for all of your assistance!