I started building a mini rat bike today using a beater 1977 z50 soft tail. After looking around at modern engine swaps available, the Piranha 140 looks like the best one. I like the price and it's 12 volts with aux power for lights.
https://tboltusa.com/store/piranha-1...nis-p-660.html
The XL125 swing arm was almost a bolt on deal! I mocked it up a little more so it looks complete. I'm ordering the Piranah today.