My buddy Chris (raygunriot) has a 73 Bonnie and he loves it. He kept it basically stock and just replaced the coils, put a Boyer and a couple MIKs on it. Great bike, and it's fun to ride. Wouldn't chop it, but cool like it is. Couple things he did was he changed out the filter plate with the screen on it for the finned, spin on filter deal that replaces the whole plate. He had oil pressure problems with it at that point. So, you might want to avoid that conversion and stick with the stock screen.
Thats what Im thinking pretty much stock, maybe some cool tires, differnt bars, maybe a headlamp fairing, nothing too crazy, definatly want to replace the drag pipes . And some how , a H.A.M.B. plate on the front fender.