I think you were the closest guess for the last mon on my team. I ended up putting LO Volc since it threatens balanced cores at +1 (AV Tang, Slowbro, AV Torn-T are all KO'd after SR), and also because the team doesn't have too much trouble with Heatran. My thought process was that MGross can help chip away at Chansey with Pursuit + rocks damage, after Hammer Arm's been revealed against something else.