Yamcha has been training with Nappa, and they have both raised their power levels (6 months ). Yamcha's power level has raised from 1,900 to 4,500 and Nappa from 12,000 to 13,750 as he is only teaching. Gohan now spend every weekend training with the Masters.
Meanwhile Dr. Gero has now received intel on Vegeta, Nappa and Kaoken and so has decided to experiment on the saiyans physiology by finding Raditz. Dr.Gero hasn't yet figured how to develop an android with a power level beyond 5,000 but notices as he revives Raditz that his power level is raising dramatically even before the full power of the Android is applied. Raditz's powerlevel at death was 1,500 battle boosted to 2,000 his revival Zenkai boost 3,000 combined with this Android enhancements actually equal 12,000 despite my math equally 9,500 because his biological body reacting to the enhancements adds another 2,500. Mecha-Raditz also has both power absorption hands. Dr. Gero has increased the number of spy bots he has so he can be up to date on his enemies abilities. Because of this he knows Nappa's powerlevel is still above Mecha-Raditz but is curious as to how well his memory wipe techniques have worked and feels that because Mecha-Raditz will have limitless stamina and the power absorption hands that he may have a chance against a more powerful opponent. Basically just using him as a test.
Dr. Gero this time sends a duplicate of the fully mechanical Android with a powerlevel of 5,000 that Yamcha fought in https://comicvine.gamespot.com/forums/fan-fic-8/alternate-dbz-part-5-what-if-yamcha-didnt-fall-to--1895053/#3 (part 5) but this time with both power absorption hands and an updated data base of counters for enemy commonly used techniques, with Mecha-Raditz to directly attack Nappa and Yamach. As the fight begins Nappa and Raditz square off and Yamcha and lets call him Android10 square off. Upon first hit between the saiyans they both get a feeling that they know each other. Nappa and Yamcha were training not very far from the Kame house and it happened to be a Saturday. So Shen, Roshi and Gohan are watching the fight from a distance and are the only ones that do know who Raditz is and what Nappa's relationship to him is. The Masters have been keeping an eye on Nappa hoping he dosen't remember that he wants to basically kill them all and that he could. part 5.5 will be continued