Tank identification

Hi, I could use a little help identifying the purple tank in the photos below. The guy I bought my 76 KZ900 from threw the purple tank as part of the deal and said it belonged to a Z1. I was planning on using it instead of the original tank. But it doesn't fit. I'm thinking it may be from a KZ650 or something. I am submitting some photos for inspection. Anyone recognize what kind of bike it belongs to? I'm not even sure if its a Kawasaki tank.

The black tanks is the original on the bike.






As you can see for the picture below, the mounts are way different between the two tanks.

1976-1980 KZ750 twin, I have several if you need another one

Thanks for the info. Wasn't expecting an answer that fast. Thanks for the offer but I would like to get rid of this one instead. I had it filled with vinegar for 2 weeks in order to clean out the rust. Came out beautiful, but for nothing. Thanks again.