I had a 1N Southpaw that I no longer use, but this is my 1C southpaw. 4 large lasers and 18 heat sinks. Pretty obvious what to do: shoot the Large Lasers. I've bound the chest to right click and the arm to left-click, clicking both is alpha strike. Use your right arm as a shield. Southpaw Alt Config A Here's my alternate configuration A. Bigger engine, more DPS, but shorter range and smaller alpha. (Alternately, you can take off 1xDHS and 1/2 ton of armor for AMS+1 ton ammo, or take off 2 DHS for AMS+1 ton ammo+1/2 ton armor). I came up with this build after realizing that the beam duration + cooldown totalled the same for LPLs and MLs, making the LPL+ML combo actually very potent. Out of all my Dragon builds, this is my new favorite (well, tied with my FlameC/20 build). The DPS it dishes out is incredible, and most people will go for your right arm first, which just takes a couple DHS away.
I'm looking at doing an Alt Configuration B and C, where B involves a 350 XL, 4xLL, and 14 DHS; and C is my LPL/ML combo with a 360 XL and 17 DHS.
I was looking at tweaking my Harasser build, which is similar to the Southpaw, and ended up with something halfway between the Alt Configs B and C you mention: You'd have the slightly faster firing LPLas+MLas combo in the arm for close combat and 2 LLasers in the torso for longer range sniping. A 360 XL version would basically just be sans AMS. Gonna try it out and see what happens. Otherwise your Alt Config C sounds quite interesting.
5/5, This is how I would run this build. I mastered this chassis with this build after the quriks, and it works very well!
Another thought on this one: Sacrifice one LLas to be able to use an entire side as a shield. Since this thing doesn't get the heat efficiency bonuses like the STK-4N, it can run pretty hot...keeping the lasers on the torso means it has a high firing point (always nice), and it still has 1 LLas on the arm for sniping UAVs when needed. Can still move at a decent pace thanks to the STD300, but it trades a bit of DPS for the ability to survive with the RT/RA as shield components. All heat sinks on the left side, because why wouldn't you when the weapons are all there? Kept the BAP, but you could easily drop it for a MLas or another heat sink and some armor.
I've been running this as a support mech w/ 4 ERLL instead of standard Larges. Range module + chain fire -> laser-based dakka out to 800+