Typically, the "heading up process" starts at the rear of the action body. In the vertical plain.
I use a plexiglasss cut-out approximating my desired stock shape, and I trace it on the blank.
In that moment, I am identifying figure, knots, grain flow, and sap wood, to get what I want where. Slide the plexi glass around, see what is possible.
Here's where that impacts you.
The comb angle vs the plane of the rear of the action.
Your first plumb cut sets up everything else behind it.
Don't screw up the blank with the first cut.
When you have that plumb cut made, you can start letting in.
I cant tell from your pictures, but I think you'll be going ahead first, and then letting the top strap down into the blank.
Check out some You tube videos for AyA or Purdey's, they show enough heading up to see how to avoid a first cut malfunction.
