Eventually I could beat it with the build I have now. Unfortunately my weapons only do 1 damage per hit on the mech, so it will take me 1345 hits (448 turns).
On a level 30 build the highest damaging item I have is 78. With the kits on this mech that's 33 damage per hit (without a shield) and eventually I will run out of bullets for this item. Other than that my other weapons hit about 10 damage per hit and my droid hits 1.
39 damage x 6 turns = 468 (6 turns for the ammount of times I could use my bullet weapons in a suitable build.)
From there on out I manage to deal about 10 damage a turn.
So 6 turns 1345-468=877 (6 turns)
Then 877/10=88 turns.
so in total even with a top level 30 build (that i know of) it would still take me 94 turns to kill this mech... and that's only if I manage to keep this mech overheated else I have no chance. Not really worth 1.5k SM (or whatever the reward was).