Yup, that butt has seen better days. You may find
Mike Yardley's book Gunfitting helpful. There is a pictorial
featured here that's interesting. Sadly most of the best stock making books are no longer in print and extremely hard to find.
Your method may differ but I would begin by piecing everything back together then tracing the outline of the butt on a knot free pine board. A chunk of 2x10 or 2x12 will be plenty wide enough to make a practice piece. One board may not be thick enough but two glued together will be. To judge the letting for the receiver and locks try lining the original with clear plastic wrap then use modeling clay to make a mock up of the original. Simply pack the clay in and around the letting. Be sure to have enough plastic wrap sticking out around the edges to pull the mock up out. The mock up will provide solid reference for the receiver end letting.
Stock making, obviously, is both a skill and an art form. It takes practice and patience to learn the skill and develop the art. Practicing on a pine board is the best way I have found to do this.
Keep us posted on your progress?
Hank
