Personally I would go with the max engine and have a couple backup weapons in case you lose the arm. Here's my idea:
I agree, had not seen this build before and did it myself one night. I don't like putting all my firepower on things that get blown off. So mine went into the torso-means I have to be more careful of elevation when engaging but having these two giant lasers pays off big time. Essentially an energy AC20 on something small, agile and nasty.
If you increase that engine to 255XL (same weight as 250XL) you get a free DHS in the engine which benefits from the improved engine cooling so can go: Particularly relevant build with the new +30% LPL Range, -20% LPL Heat Gen, Laser Duration -10% quirks. I shifted the armour a bit to reflect the new +12 LA Armour. Might as well shield that side a bit!
I know its not the OP's but been running the RVN-2X fit of @fx8230 this evening and it works very nicely. Just a pity that its not got slightly more cooldown bonus. The first 4 matches in it: Nothing exceptional I know but really solid and sometimes doing 400 damage+ over the second highest on the side.