I also bought a z50 frame from this guy; thank you for bringing it to my attention autofull. I am almost positive that the frames he is selling are street legal and can be registered. Heres why:
I bought a new lifan 110cc CT70 copy bike that has the exact same frame, and the exact same "looking" MSO, as the ones this guy is selling. I bought it from hooperimports and it came with an MSO also. I was second guessing the MSO all the way to the DMV, but when i took it there i had no problems. It took a while but i walked out with a tag and drove the bike home. (you dont need insurance in florida to tag and register a motorcycle).
So for anyone else that got one i am almost positive it will work out for you.