My suggestion.

Start with a Whidden V Black for your action. Place this in a soft wood (pine, maple, bass, whatever) in the approx final shape. Coat action with release agent and coat rough stock with wet fibergalss (or even carbon fiber/polyester) and place action in and bolt in place. Wait to hard and remove and sand to final dimensions. No fillers needed.

This is how they used to make stocks for silhouettes as weight was a premium.

Your time, your choice.

Larry
Tinkerer