Any of these arms are nice pieces, and make me wonder if they would fit onto a more standard dreadnought for some conversion work. The Praetor Armoured Assault Launcher is just huge. It looks like just the launcher itself is nearly as large as a chimera.
Experimental rules for the Kheres Assault Cannon http://lyris.games-workshop.com/t/92430/7211474/5157/0/
Experimental rules for teh Praetor Armoured Assault Launcher http://lyris.games-workshop.com/t/92430/7211474/5711/0/
The Praetor Armoured Assault Launcher combines the armoured might of the Crassus super-heavy hull with the long-range capabilities of an immense multiple missile launcher. The design, sanctified and approved by the Adeptus Mechanicus, was discovered deep within the cogitator stacks of the recently-reconsecrated Forge World Zhao-Arkkad.