KyFlinter: so, if I understand- the square part to the right of the hinge; that will be turned down at 90 degrees and attached to the side of the cut or inlet area in the stock. This will mean that only the oval portion will be visible. In looking at the side of the butt of the stock the hinge will be at the bottom. This I believe is typical.
The inlet of the stock will need to be set in around its perimeter say 1/8" to create a little shelf for the outer edge of the oval portion of the lid to rest upon/against. This shelf will be also inlet the thickness of the lid so that the lid is even with the rest of the stock's surface. This inlet should not be so tight that in lifting the lid it could pull or chip away a surrounding portion of the wood.
Now about the spring.
Option 1. If a cam type spring is used then you would normally need to slip your thumb nail under the lid to lift it. In order to do this I would think a shallow dished area would need to be formed in the wood at the top of the oval lid.
Option 2. If a catch was used to hold down the spring, then some sort of catch devise would be needed- but where would it be located and how would it work? I realize there are probably endless options- all I want to to know what would work and be fairly easy to accomplish.
And...I realize it may sound like I am answering my own questions but I am stating what I think is correct. Any help with whether I am right or wrong is appreciated. Thanks.