Let's play on the "the Dragon Ball Gang hadn't met each other for quite a while and Piccolo is still a villain". Which will lead us to create stories where only some of the cast are teaming up with Goku for a given threat. For example: I'd put an arc where Colonel Silver (a well designed yet a wasted character) is the main villain, taking place 3 months after Goku and Chi-Chi's wedding. Silver obtained new technological enhancement for himself (sorta like that Pilaf Gang GT's pilot robotic suit) from Parfe,a former disciple of Dr. Gero (whose name is a pun of "Parfait"), and some new underlings who help him in tracing the Dragon Balls to gain World Domination (with the Dragon Radar they've stole from the Pilaf Gang), they begin their chase for the goal under the heroes' nose and once they've obtained 5 balls Bulma will get up on them and will send Yamcha, Goku and Krillin to do some sniffing that will eventually lead to confront "the new and improve" Silver himself and will take him out. Edit: Don't forget, even against Raditz Goku had a tough time flying, so in this point in his life don't expect him to be able of performing/demonstrating his marvelous Z and beyond techniques and abilities.