Initial info and data for neck / string spacing / bridge strings span:
The string spacing / span of this guitar's bridge puts strings 1 and 6 at the edge of the frets at the high end of the fretboard. This makes a full spectrum of modern playing techniques a bit awkward. So I suggest some modifications to make this guitar's bridge or another bridge and / or plate compatible with this guitar and provide a better / narrower string spacing / span at the bridge and thus along the upper frets of the fretboard.
There is nothing at all wrong with this guitar's bridge and it's string spacing / span not fitting well to the guitar's upper neck width, .....but quite the opposite; It's the narrow upper neck design that doesn't match up well with common bridge string spacings of outside supplier bridges Harmony had to choose from when they realized how aggressive vibrato would become and that the non-intoneable wood bridge they originally designed onto the guitar was not well suited for such vibrato use. But even their wood bridges also brought the upper-fretboard string span to the outer edges of those frets.
The best guess I can make about why Harmony would not be more concerned about string spacing at the upper fretboard, is that general public Players playing techniques were not as advanced and aggresive as they became. Harmony's original non-intoneable wooden bridge used on the original design of this guitar, did not work very well at all for vibrato use, and it's string spacing / span was also too wide for the narrower design of the upper neck. The original design bridge would wobble and otherwise displace itself with vibrato use, so Harmony wanted a bridge that would work better with the vibrato. I feel rather certain that Harmony acquired the intoneable roller bridges for their last runs of Bobkat and Sihouette guitars, from already existing Japanese parts sources, rather than tooling-up to make a wider neck or narrower bridge; And Harmony likely felt that a slightly wider upper fretboard spacing was an acceptable trade-off for an already existing replacement bridge that would work better with the vibrato. I also think it indicative that this guitar was made just before the period that Harmony started jobbing (contracting) the manufacture and branding of their guitars to Japan, slightly ahead of Epiphone doing the same; So Harmony probably saw their economic demise at hand when they decided to use these Japanese bridges on the last of their USA made guitars.
I recommend Maximum and Minimum string spacings / spans listed below that will allow for more playing tecniques. HOWEVER, there are some problems in seeking that string spacing / span with current common replacement bridges:
Most modern bridge makers base their geometry upon the wider bridge geometries of Gibson and / or Fender bridges; So the string spacing / spans of common replacement hardware do no better in matching the narrow neck of Harmony guitars of this guitar's period. Where narrower string spacing / span can be found on a replacement bridge and still be similar to this guitar's bridge, then their mounting plate & posts geometry is most likely to be different than the measurements of this guitar's bridge mounting plate / posts;
So modifying the upper bridge assembly mounting holes, or the body mounting plate or it's posts would more likely be required than finding all the geometry to match up with this guitar's mounting plate / posts.
I am still in the process of searching the data of suppliers of bridge and bridge parts, to be able to make the best suggestions for getting a narrower string spacing / span onto this guitar's bridge.
Data is being compiled and drafted on this page to provide for both my search and for future searching should I not be able to find a proper solution in a reasonable amount of time.