you have to change all ,stator flywhell and cdi, also have to change the timing point with the 61 x stator.or you going to have problem
we just build a b1 with 760 B2 engine with my father (not the first one) and still running the 760 electrics and works pretty good with good carbs setting, B pipe, Ada head and 144 pump( for the moment) and have 14/18 solas prop.
the way to change to the 701 electric is good if you want to run a MSD cdi , if not it s not necessary you can keep the 760 electric.