This thing packs a punch, the SRMs and the AC 20 are just mean. The large lasers offer good range support until you hit them in the face. the 340 engine is faster as the stock one so you can reach your targets earlier. The Medium Lasers in the center are your zombie mech, only fire them if you really have to, but these boys are the difference between this mech and the mighty DDC.
Vaan, you can remove the CASE from your right torso, as AC/20s don't detonate when crit like a Gauss Rifle does.
To the OP, I'd move the AC/20 ammo from the arm to the head and I'd match the ammo type per leg. The current Ammo mechanics don't pull equally from the ammo bins. Instead, they work one bin at a time. With your build, if you run through half of your SRM ammo then lose your left leg, you will have no SRM shots left. Stack like with like, that way you'll have a better chance of having weapons that will fire in the event of leg loss.
I'm a little wary of 21 ammo on the AC/20. I think with a 325 STD engine you could fit more ammo and armor on, for not a huge loss of speed (57.9 instead of 60.6). That 325 engine might just let you get that...one more thing...
I used to run the OP build, but I enjoy other builds more. That said, it is a fantastic build. 5-5 stars.