This engraving machine was designed by Benton around 1860 or so. This invention was an essential step, with it identical punches could be made in series.
Before this punches only could be made by hand, and when a new punch was needed, it could not be made perfectly identical.
The original patterns were made first in wax, the pattern was taken out, a thin layer of metal was added by electro-deposition, and the result was filled with molten lead.
I think photo-polymere would do quite fine for producing the patterns. With modern design-programs it should be possible to make the perfect line-pictures of the characters.
That manual... I do not know how far they are with this. But the place to investigate this would be the Type-archyve in London UK.
When you would be able, you should visit this museum and meet Kumar, the very man who preserved all this knowledge.
I know a few other places where Benton engravers are preserved, I've seen a few of them in Swiss, at the Parnassia printery and typefoundry. They also make matrices, but this is done by direct engraving, with a precision pantographe, as far as I know.
While producing new Monotype fonts, you do need in mind, the unit-system Monotype used.
The wedges were adjusted to this, and the widths of the characters were equal to whole numbers of units.
However, with the use of computer controlled casting, the program can adjust the width of all character if needed, and even a correction of a quarter of a unit (or less) is perfectly possible. The only disadvantage is that each correction needs two machine-cycles, and would slow down casting a bit. But, who cares about mass-production with a project like this ?
Jan van Krimpen did complain a lot about that unit-system... But computer controlled casting on a monotype will give us all the freedom we need.