The easiest solution is to find a replacement part in good condition.
If that's not possible, many Hondas from that era had the same size shaft and splines, as did a bunch of Yamahas including RD350 and so on. It is possible to cut off the damaged end, and transplant the end from a different bike. I had to do that on a TZ350 a while ago and used a CB160 end which was drilled and pinned and silver soldered. It was dead straight without a step at the joint.
That was a lot of work, but at the time I couldn't find a replacement part so I had no option. Hopefully you will find a good used one.