That is a sweet look!

great tank!

From which bike it comes?

I have no idea what the tank was designed for.  It's obviously a custom made tank from the 70s, and because of where and how the gas cap is located, I'd guess it was for a "standard" type.  On old Triumph, Honda CB...something along those lines.  I love the way it looks, but it only holds 1.5 gallons...if I push it close (and then I have to be careful about going up hills or accelerating too fast or gas leaks out the top...).  So I typically put about 1.15 gallons in it.  The advantage is that I get to stop more often and hae people ask what it is.  

When riding, it feels like I'm leaning more forward than it loks like in the pictures.  My tailbone doesn't feel any pain at the end of 45 minutes of riding, but my lower back is killing me.  I don't have the best posture to begin with, and this really just makes things worse.  In all honesty, the buckhorns were better for my back than the Z-bars.

My next project  is to rework the exhaust.  I want it to split into 2, then sweep up into stacked fishtails, ending about the same height as the top of the rear fender.