http://i.imgur.com/s6wWHtx.jpghttp://i.imgur.com/UUxYook.jpgA Murder without lance-refit looks like a carnage with prow lance. No prow lance = carnage.
The "incorrectly built" Devastation could be a Hecate...does it have 2 dorsal lances?
If not i would suggest to give it 2 dorsal lances and convert the "incorretc Devastation" into a Hekate.
Instead of giving one sides upgrades they don't really need - consider using some imperial ships for the chaos side (traitors).
"For every 1,500 points in a Chaos fleet, one cruiser from any Imperial Navy fleet list up to 185 points and/or up to six Imperial Navy escorts may be taken. Special weapon rules, Nova Cannon, Chaos Lords, Chaos Space Marines, Chaos ordnance or Daemonship upgrades may not be taken for Imperial Navy vessels used in this manner, and cruisers suffer -1Ld for going renegade. Imperial Navy escorts need not be in a single squadron and may be interspersed within other Chaos escort squadrons if desired. These vessels do not count as reserves; they count as Chaos vessels in all respects. "
- FaQ2010
the "upgrades may not be taken" part refers to upgrades only, not for base armament.
With a chaos spacehulk and some imperial vessels on the chaos side you should be fine without "using everey possible upgrade". And you still have the option to form an imperial fleet and let them fight on the chaos side. No background issues with that, traitors are everywhere.
For list building stuff: i play only eldar, someone else have to answer that question. ^^
Edit: What do you mean with "imperial battlecruiser hulls with forward weapon battery glued in" - as far as i know, there are no imperial BC with some kind of forward weapon battery...AC and BC hulls use torps or nova, and some rare cases use lances (protector) or nothing (jovian).
Do you mean one half broadside are already glued-in weapon batteries? In this case you could build Mars BC's when you add the launch bays. Or an Armageddon BC with lance/wb broadsides and a nova cannon (the nova cannon upgrade for the armageddon is in the FaQ2010).
If there are no broadside weapon batteries, you have to be more creative - in this case i would suggest you remove the nova cannon (or build a power ram from it) - then you could convert with lance and launch bay broadsides to Dominion class BC (use reserve rules and take them from the Bakka list) or with only launch bay modules to Jovian class BC (use reserve rules and take them from the Corribra list).
Another way would be: Remove the nova cannon and the dorsal lances (to downgrade the hull from BC to AC). Then you could build a Gothic with lance-broadsides or Protector with lance + launch bay upgrades (the Protector needs 2 prow lances - maybe you could use the removed dorsal lances here somehow).
Edit2: if the BC hulls really have prow weapon batteries they must be from - i don't know - post a picture and we will find it out.
