Now, as far as castoff,
I have agonized over this since I first looked at the stock.

I have always added some cast-off (about a quarter inch) on rifle stocks I've carved on; BP or cartridge rifle. And it has always worked well for me.
Now I'm wondering, since this stock was pre-shaped, maybe they added a bit of cast-off during shaping.

I can't imagine they would have, but I guess I'll run a line and make sure.
After reading Flintlock's post I had decided to add a bit of cast-on rather then leave it straight. Then I started thinking. This is a right handed rifle. At my age, It isn't likely I'll be hunting with it for the next 50, um,

25, uh,

10 years...

so I'll do what I normally do with RH guns! Add a bit of cast-off!

Make a decision and stay with it I says!
Sides, if I can't shoot this one and I don't get my vision back I can always build another rifle!

After I stock my 45-120 and 50-140 Handi's that is!
Yesterday, while sitting in the man cave looking at the stock and lock and thinking, and thinking and looking, I did a couple more things.
First I made a pattern of the lock plate and penciled it on the stock's lock flat pretty much in position. then I marked the position of the sear arm and from that the final postion of the trigger. This let me measure the length of pull which i marked at 13 and 3/4 inches. That done I measured the drop at the nose of the comb, and heel at the LOP line.
I can work with the dimensions of the stock as cut, but doing this made me realize how much flexibility these precut stocks take away from you.

I would imagine those "fully inlet" stocks are proportioned for the mythical "average" man.

Something to consider...
I also did some measuring of the ram rod cutout in the forestock. The web between the barrel channel and the ramrod channel was a good 16th of an inch, actually pushing an 8th of an inch to thick. so I started digging through my round files.
I couldn't fine the already bent one, however, I did find a new Nicholson of the correct size. But I can't bring myself to bend the tang of that file so I can use it in the groove.

I'll think of something...
And while I'm thinking, I'll think about doing some more shaping of several areas of the stock. Maybe not though.

This thing is so close to the final dimensions I may just wait and do it all together after everything is mounted!
Sides, I want to play with the lock. I got it apart, but I ain't takin bets on getting it back together again!