One of the coolest bikes I ever saw, and should have bought, was a 1987 Kuwahara Cascade that had a sloping top tube... this would not be unusual except it was a handbuilt model with a lugged frame.
Odder still as I have a 1987 Kuwahara Cascade with a conventional lugged frame with a level top tube but other than this the parts spec was identical.
This means they made two models with the same name and would have had to make custom lugs for this second variant.
Mid eighties Kuwaharas are awesome bikes btw.