Hello, I think on you tube Lebaron Bonney had a video on that . A Roadster might be similar, think most of work is done with a wood chisel. Hopefully you will get more replies than mine .
I use a hand held belt sander with a 1-inch wide belt but I have to be careful to shape it right. The chisel is the tried and true method but care has to be taken with it too.
I make 1/4” plexiglass templates and use small screws to attach to wood. Then a router with bushing and trace inside my template. Small mounting screws can be filled and hide.
The cuts are very clean and precise.
A soft start router works best.