[ Ref. Dan Dickins in 141114 MMDigest --

Dan, I have made a few of these over the years by cutting thin sheet
brass into the proper configuration.  Even if you can't determine the
exact shape of the now deteriorated plate you can use either the photo
from an old Player Piano Company catalog or use the basic shape from
another governor you may have lying around.

The slide generally has a hole to start the slide slot that is about
3/16" in diameter.  The slot resembles the bell of a herald trumpet
that starts out parallel and then flares out.  There is also a second
5/32" hole on the other side of the "trumpet" slot that allows a small
amount of vacuum to pass for the reroll, I believe.

The brass is soft enough to be worked with a drill press and a hacksaw.
The sides can be smoothed out using a triangle file.  It is held in
place with escutcheon pins (small brass nails) but usually a bead
of burnt shellac will seal it in place before the pins are inserted.
I would also suggest coating it with lacquer to help keep the leather
facing on the slide valve from reacting too soon with the brass.

Good luck!
Norman Cantrell