Smooth On makes a silicone mold material that will withstand the heat of casting in pewter. I have not tried this so am not sure of the resolution of pewter but if I had to make these sideframes this how I would do it.
https://www.youtube.com/watch?v=D_BGMBmc7Pg
Good idea to reuse the bearings but new ones could be machined with oilite bronze.
I think a one part mold could work but the video shows how to make a two part mold.
Pete