If you're having to retighten the rear hub nuts every couple of hundred miles then I think there is definitely something wrong!
If the tapers are lapped together & the original style keys replaced, as outlined in my earlier post, there shouldn't be any issue with normal road use.
Personally, I wouldn't replace the original castle nut & split pin as they are a long used & reliable locking method.
Just my own opinion/experience of the factors involved, others may have their own take of course.
Regards, Luke.