This is one of those builds that I had to ask "really? This hasn't been posted before?" SRM4s and MPLs are, in my opinion, the best missile and energy brawling weapons for IS Mechs. SRM4s are more accurate than 6s and more efficient than 6s with Artemis, and MPLs are may not as good as LPLs, but you can get 3 of them for less weight than 1 LPL. Your build has nearly full armor, especially where it counts (full on everything but legs, which have enough). It has decent cooling, and a max engine. This is an option if you're willing to sacrifice speed for cooling. It sacrifices 5 KPH to put on another 2 DHS, which I guess isn't much. I was at 99.5 so I put half a ton back on the leg armor, but you could take it the other way and get a third extra DHS. In the end, I'd probably go with what you posted, just was curious to see how many heat sinks you could fit on by dropping the engine and dropping endo-steel. Overall, great build, surprised it hasn't been done yet on MechSpecs.
Update to my previously posted alternative. Drops the lasers from MPLs to MLs, to gain an extra kph, an extra DHS, and an extra half-ton of ammo. Not sure the reduced burst is worth it, but it's an option for those who like to maximize heat efficiency.
3/5, XL400 is a waste of tonnage, but because this is a max engine meme I'll ignore that fact. What's left is an oversized kintaro with a fragile engine.