Changing the font file's creator to LWRR should have worked. It turns out
that there is an anomaly in the BNDL resource in the LaserWriter 5.2
drivers that keeps the necessary information from being copied to the
Desktop file of a disk.
Specifically, the LaserWriter 5.2 BNDL resource specifies FREF resources of
IDs -8185 and -8186 for the two types of downloadable font files. However,
these FREF resources actually have resource IDs of -8189 and -8190. Since
the BNDL entries do not agree with the actual resource IDs for each FREF,
the information is not copied by the Finder to the Desktop file, and the
file icons remain blank.
If you want the icons to appear as they should, you can use ResEdit to
change the resource IDs of FREF -8189 to -8185 and FREF -8190 to -8186.