Molds- Re;Raulduke.
Hi;
The molds you are speaking of will be easy .Have you ever used Foil-Chrome on model cars? This is the way you can do it ,that I have used many times for missing parts on the Museum's locos.
You take foil, Baking foil is best ( it's Thicker ). Now you find the part you want to make. Carefully emboss the foil, using the part as a form .Believe it or not I use PAM as a mold release.I decant some and taking a soft paint brush I carefully go over the mold with it.
When done , sit the foil in such a way the whole thing will be supported . You might want to try oil free clay and push your part into it .( this works too ). Now take two part resin and mix well. Carefully allow it to run into the part cavity and let it set up.
Then after set-up let it sit overnight at room temperature. The next day carefully remove from the mold .There's your part. This has worked for me and I do hope it works for you. Tanker - Builder