[806mtson]

So, Stacaesar's Mecha and overall basis in design being a reference to Battle Fever J is most likely due to Battle Fever J having the first Giant Robot in Super Sentai with the Battle Fever Robo. This is directly referenced in his mecha being called "Battle Caesar Robo". It also takes cues from Choudenshi Bioman's Balzion, which might be the first Evil Mecha. I can't really judge this, as there seems to be a lot of evil Mecha according to the Wiki.

So, it seems as if each Ranger/Mecha in Kikai Sentai Zenkaiger must be a reference to a Milestone in the History of Super Sentai. Zenkaizer is based upon Himitsu Sentai Gorenger, the First Super Sentai. Zenkai Juran is based upon Kyōryū Sentai Zyuranger, their main Mecha, Daizyujin, and the Red Mecha, Guardian Beast Tyrannosaurus. Zyuranger was adapted into the Original Mighty Morphin Power Rangers. Definitely a Milestone. Twokaizer is based upon Kaizoku Sentai Gokaiger, a monumental Milestone as it was really the First Super Sentai with Legend Sentai Mecha. The only other Super Sentai that I remember having Legend Sentai Mecha before Zenkaiger is Ressha Sentai ToQger. Even if it's just in the Toyline, they had a ton. Zyuden Sentai Kyoryuger, Gokaiger, Tokumei Sentai Go-Busters, Tensou Sentai Goseiger, Engine Sentai Go-Onger, and Samurai Sentai Shinkenger. Heck, they even included Kamen Rider Den-O's DenLiner as a Mecha. But let's get off this tangent and figure out what milestone could Zenkai Gaon, based upon Hyakujū Sentai Gaoranger, their main Mecha, GaoKing, and the Red Mecha GaoLion, Zenkai Magine, based upon Mahou Sentai Magiranger, their Main Mecha, MagiKing, and the combined form of all of the Main Mecha besides the Red Mecha, MagiDragon, and Zenkai Vroon, based upon GoGo Sentai Boukenger, their Main Mecha, DaiBouken, and the Red Mecha, GoGo Dump. I know that TwokaiRicky and TwokaiCutanner are basically Easter Eggs to a mistake Gokai Silver did in one episode, I think. Someone else can correct me.
Meanwhile, I think that the Mecha/Kikainoid that will give Juran his "Super Zyuran" Form might be based upon either Abaranger or Kyoryuger. I am leaning more towards Kyoryuger, as Abaranger is older and was part of the basis for GoZyuDrill/GoZyuRex/GoZyuJin. Even though GaoLion and MagiDragon were the basis for Mecha in Gokaiger, I still think Kyoryuger is more likely.
Side Note/Tangent
Though, this really raises a question in my mind, "How would the Super Sentai after Gokaiger be involved into GokaiOh?" Basically, "what would their Greater Powers be?" MagiDragon is the Greater Power of the Magirangers. The Dekamachine Patstriker is the Greater Power of Tokusou Sentai Dekaranger. GaoLion is the Greater Power of the Gaorangers, Karakuri Warrior Fūraimaru is the Greater Power of Ninpu Sentai Hurricaneger, looking more like Shinobi Machine Tenkuujin. And Engine Machalcon is the Greater Power of the Go-Ongers. The other Greater Powers are the Variblune of the Gorengers and the Mega Winger from Denji Sentai Megaranger. And GoZyuDrill/GoZyuRex/ GoZyuJin is a combination of the Powers from the Zyurangers, Mirai Sentai Timeranger, and Bakuryuu Sentai Abaranger. So, I wonder what the Greater Powers of the Super Sentai after Gokaiger could be. Kyoryuger has to be either the Zyudenchi as a whole or Zyudenryu Gabutyra. He is one of the most important Mecha from Kyoryuger. The Greater Power of Kaitou Sentai Lupinranger VS Keisatsu Sentai Patranger would likely be the Lupin Collection as a whole or just Good Striker. Imagine Good Striker combined with GokaiOh.
End of Side Note/Tangent