I tried using "cut with surface" but that only seems to allow picking a surface that belongs to part being edited. Should I look at using one of the "mold" features?
Yes - however, be very cautious. Sometimes it is best to break all relations after editing the part. Otherwise you will get rebuild errors if the original part used to make the cut is missing or has changed. Have you tried creating a 3D surface from the other part?
When you are editing a part within an assembly on a particular surface/plane then you can project geometry from one to another but I am not sure you can actually use another parts volume or surface to actually make the cut. Perhaps Mold can do this.
Try, editing the part you want to cut in the assembly context that you have the surface you want to use.
While editing the the part you want to cut,
See if How to use one Part to remove Material from another Part in an Assembly? will help.
Thanks everyone for your replies and suggestions. I'm looking at using Smart Components to do this.
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