From what i read, japanese choppers were popular in North America the 1970's (i wasnt born yet). A buddy of mine bought this 78 CB750 chopper (bobber style) a year ago and has gone through the process of stripping it down and re-engineering and rebuilding the frame.
Here's a few pics:
He built the oil tank using scraps of steel, welder and alot of patience. The stock fittings were cut off the original oil tank and welded on... the mounting points are cut from angled steel.
Frame was hacked, smoothed and stretched 4 inches...