The inside of the bottom bracket shell shows a square cut chain stay end. I would expect a custom frame to be mitred. The square cut is typical of a mass production model, though I've never had the opportunity to inspect the inside of a Fuji Design Series.
However, we have seen atypical Design Series bicycles before. I've seen one serialized October 1985 with stay chroming beyond the brake bridge, atypical livery and a pump peg. I'm not sure if these are indicators of a custom build or a foreign market model. I'm leaning towards the latter, as I doubt they were doing custom decals.
We know that Fuji went to rear brake cable routing under the down tube on American models in 1987, so it's conceivable they were using it slightly earlier on foreign market models. Regarding the size, it's possible that they are meant to be stops and used with necked ferrules. The presence oftwo eyelets, as opposed to three, also suggests they are stops.
Even assuming it is custom, I'm surprised by the lack of decals. By this era, Fuji was clear coating over decals, so they wouldn't be easy to remove. IMO, the lack of decals suggests a very high probability of a repaint and, ifit's been repainted,that opens up the possibility of changes in fittings.
Regarding the steerer tube stamping, 6.C is a date code, indicating March 1986, so it's a good match with the frame.
I do not believe that Fuji 9658 is Ishiwata 019E. I believe that 9658 corresponds to the four butt gauges and if so, corresponds to Ishiwata EXO-M. If Ishiwata 019E had a four digit Fuji number, it would likely be 8547. An Ishiwata 019E frame would theoretically use a 27.0mm post,while a Fuji 9658 frame would theoretically use a 26.8mm post. Unfortunately, these are so close that things like corrosion, scale, burrs and distortion can easily result in misinterpretation when trying to measure the tubes and could result in an undersize post being employed. Similarly, overzealous reaming, could require an oversized post.
The bottom line is that I can't say if it is custom, though it may have been customized after being manufactured. There's also the distinct possibility that it is simply a foreign market model. However, I do think it is a repaint.
Last edited by T-Mar; 10-26-17 at 08:28 AM.