Originally Posted by
nishikiwhat
. . .
The seat tube (not the BB) has the serial number stamped on the bottom part - GS71399
The fork (hopefully it's the original one) has "Ishiwata" stamped on the steerer tube
. . .
Hello nishikiwhat, welcome to the forum.
The serial number format and location are probably not for a Nishiki.
More likely this is a frame made by Maruishi. Maruishi was contracted to make frames for several marque names including Nashbar.