The Neatmkfn program creates Neatroff font description files from AFM (Adobe Font Metrics), TrueType, and OpenType fonts. See the output of "mkfn -h" for the available options. Note that for OpenType fonts, Neatmkfn cannot obtain glyph bounding boxes accurately. Therefore, if you plan to use a font in Neateqn blocks, convert the font to TrueType and generate the font description from that.
The included ./gen.sh script invokes mkfn to create a complete output device for neatroff. Change the variables in that file before running it.