The taper angle is the same, but a different size.

If it's of any use, I fitted a hybrid 125 road bike/RS250 NF5 ignition to one of my 300's. Basically NF5 charging system, through NF5 reg/rec, into NSR std battery. Stable at around 12.1V with engine running and revving, but not with lights on, indicators flashing and horn going. It might have struggled with that.