I did this change years 10 years ago. The wiring in the headlight got ripped out. I just rewired everything and tucked it all between the flat side tanks that I put on my 1990 FXRS. I drilled the stock lower tree to mount the headlight as you mentioned as well. Over the years the bike has gone through many changes but none as serious as now. I've since cut the front frame up and converted my trusty FXR into a FXRC, C is for "Chopper", 9 1/2 ft. long bike, but still a HD. Good luck on your project.