Gary - I think this is an excellent question. Sadly, there is but a single example for measurements in my collection; an 1893/95 DWM factory sporting rifle in 7x57. The edges or "thickness" of these panels, from top to bottom, are parallel for all practical purposes. The sides do taper in thickness slightly from rear to the front; an approximate 45mm thickness just above the triggers to a 43mm dimension above the front action screw. This is not apparent (without using a caliper) while you are admiring the aesthetics of the stock design.
I'll try to post a link showing photos of my rifle.
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=207108#Post207108
