I must apologize I guess I miss understood . I thought your question was on the mortise and how it came to the forestock . You have not said if this is a full stock leman Trade rifle or a ½ stock ?
If I read your question correctly its:
does the forestock hold the same dimension IE side to side thickness forward to the entry .
Again that depends on the design of the stock .
Normally the forestock will hold the same detention on the sides and bottom from the lock mortise forward . . Its common also to have a narrowing to the nose cap , if you have one . This however should be gradual and not abrupt .
Your lock mortise should be raised above this plain .
The bottom should be rounded not square with rounded corners .
Now what will change is the area right along the barrel when viewed from the top . While the dimension of the forestock stay or gradually tapers in width, in this area the shape changes greatly .
This would be that for say 4 inches or so in front of the mortises the wall thickness will be ?? Say 3/16 ,,, it will then start to narrow down and within another 8 to 10 inches be but a fine line say of 1/16
Now how fine that and fast this gets depends on your eye and what you like . Keep again this is the area on both sides of the barrel , just in front of the mortises , when viewed from the top . This also concerns shaping of this area with both side having the same contour
The later , “common place” plains rifles, were often blocky while the earlier long rifles have fine lines of grace . .
Normally I figure on having to take a minimum of 3/16 completely off on custom stocks . Production kits that’s more to a ¼ as normally they are way to heavy.
Once you have the lines down and the shape to what your happy with you then start the finish sanding or scraping and boning.
Once you think the stock is about ready to apply stain or oil ,,, that’s when you do your carving or engraving .
While it may look as if the carving is very raised , its not . You will find most to be 1/16 or less deep .
Another thing to remember is incise carving ,,, is much ,much , much harder then the fancy relief carving .
With relief carving a person and make a mistake and simply change the design or clean things up . With incise carving ,,, once you make that line , it very , very hard to correct and almost impossible to remove.
With Incise carving you get one chance , that’s it .
I once again must apologize as sometimes I have a hard time explaining . If im still confusing you let me know and I will make up some quick “general “drawings