It’s taken years to finally find an official picture of the Nitto B702 bars listed as the stock part on the Feather Professionals from 1980 on. But finally, here they are! I found these in the 1980 Japan’s Bicycle Guide catalog which is a goldmine of vintage Japanese bicycle parts.
The B702 handlebars, with the distinct concave crossbar, look very similar if not identical to the aluminum WIN branded handlebars that seem to be more common to find. Next task is to pick up a set of the WIN handlebars and see if the stated measurements match.