Michael,
I recently traded into a High Wall Musket with the same type butt plate having the following measurements.

Height 5.06"
Width 1.54"
Rows of checkering below the bottom diamond 9

Here are pictures of the stock and butt plate.
Side view


Top view


Back view


This is the first Musket I can remember with this style stock.

Cheers,
Laurie


falling block