Titled off engine serial number

I'm looking at a 1979 Kawasaki KZ650B that is titled off the engine serial number, not the frame. Is that common? or is that abnormal? or even legal?

depends on where you are from,but if it is a state title im guessing its legal wherever the title is from;)

I live in Wisconsin. I've just never heard about this before.

It could be a problem if you try to license it in another state. I know in Idaho they only look at the frame numbers when you get it licensed here.

I recently had an out of state KZ1000 inspected for an OH title and they only looked at the frame number. Then again, that's all that is listed on the title, so maybe they would have checked the engine number if that was listed?? I just saw a KZ1000 or 900 on eBay like this and wondered if I could get it titles (engine numbers only).