Trying to build a heroic rancor squad....any suggestions?

FO is probably easiest but you're a long way from it, and can do really great damage in a really short period of time.

Another option, but a long solo (like 30-40 minutes):
zVader, Tarkin, Palp, TFP and one other TM remover (ideally Jyn who you don't have, or Teebo, or Bistan) but you'll need pretty high speed and great critical chance on TFP. You're pretty close to this team and just need a Zeta on Vader's lead.