I bit the bullet and ordered a set of batteries for my bike.
They are the headway cells from earlier in my blog, but I have them built into two pre-constructed battery packs. Each pack is 72Volts and 30Ah and includes it’s own BMS (battery management system). Along with the batteries I have a 72volt 10 amp charger. Although I may have to deconstruct the cells to arrange them into the bike I am hopeful I can fit one pack in unmodified for all my test rides and setup.
Each pack is 495mm tall * 285mm wide and 158mm deep. This may fit in at an angle in the vacant engine bay space, and gives me real hope that if I can arrange them well will fit easily in the frame with a custom battery holder design.