First, i'm really surprised that this build works! You can do this with C or D Left Torsos, and that's the key. Two versions of this mech, SSRM and LRM versions. You can also substitute the missiles for TC3 and additional heatsink. Your heat Efficiency will be 35% then. The two shoulder level PPCs pack a good punch, the SSRMs i like for more of a brawler mech, but without an Active Probe, it's slightly gimped. The PPC work with LRMs and the weight savings allow for more cooling and a TC1, which is slightly better, plus you have some indirect fire.
late night after work shenanigans got tired of trying to fix it after a few minutes. Let myself cool off and see, it works!