This almost assuredly needs to be skilled for missile racks to deal with ammunition shortages, and I'm almost tempted to shave another half-ton off the legs to fit another salvo.
I strongly suggest to avoid 3xMRM30. You have a small engine with little speed, so you will have an hard time to get close / flank and get in the "little spread" range. Heat efficiency is garbage: you can't start a brawl against a fresh mech and win it without overheating. Coupled with heat scale, build will be useless. Ammo count is actually overkill. You could spam it as much as you like. 2xMRM40 ghost heat is manageable (~1 additional heat), with dual MRM40 you can alpha strike and fit more speed and heat dissipation. Due to MRM spread and the fact it best work at very close range, I would fit something like this.
@CarloArmato no machine guns? Take the engine down to 280 and put 3 MGs + 1 ton of ammo. With all the armor stripping of the MRMs the MGs will destroy any open component, for no additional heat. Edit: I just noticed the arm armor is completely stripped, so no point in taken mgs on weak arms. Perhas it is worth going down to MRM40+30 instead and fit the MGs with armor.