A clean conversion is technically very elaborate, since among other things an internal thread would have to be removed and pencils of the range are plug-in; in addition, a LeGrand pencil would be needed as a parts donor. Possible would be a variant via an adapter made on the lathe with subsequent press fitting; in this solution, however, the eraser on the mechanism is omitted. An original mechanical pencil in Hemingway look is thus not to be made, only a technically functioning pencil in the Hemingway body.
Related pages on fountainpen.de:
• Montblanc Writers Edition Hemingway (1992): fountainpen.de/writer-hemingway-en.htm