HGN-738 would consist of: Right arm, replace Gauss Rifle with ER Large Laser, right torso, replace Medium Lasers with Heavy Gauss Rifle, center torso, add Streak SRM 4, left torso replace LRM 20 with LRM 15, left arm, replace SRM 6 with ER Medium Laser, head, add ER Medium Laser.
Assuming this requires a different torso, head and arms I would be in favor of a separate mini or conversion kit. As I said above I'll toss in another $150 to help make this happen but I assume it will take more than that.