Yes, you know how it is with weight reduction - "diminishing returns" - more expensive for smaller reductions. :) Yes, helmet lock will come off. Yes, i have been spending so much time investigating about the sprocket. Eventually found out that XR650L is right. (And various old XR250, same.) I will probably go with Renthal or PBI alloy, never mind the wear, i will see later if it is a problem for me)...even if i add weight with a rack. The battery,..yes, i was meaning to speak to you about that. I have some A123 cells (ex-drill pack) that i bought from someone on cpf forum, around 4 years ago. I think i cannot trust them now, so...either i find more, do it like you, or just spend the money for Anti-Gravity battery.