Make a list of everything you did since it was running ok.
And don't rule anything out. When I 1st cleaned the carb, took me 3 tries to get back on right.
Your battery problem might be a pinched wire under the tank.
running hard might be from a bad valve adjustment, could've used the wrong TDC.
Or it could be that you slipped a cog when you put on the verslavy. I've never heard of it before, but possible.
Or when you had the header off, did you stuff a rag in the exhaust? Did you leave it in? Did something crawl in?
These are all things that you might say... naw, could never happen, pause, well I hope it didn't.