Add engine units and copper cables to the recipes since the gravity assembler can't craft either of them. Engines and cables are relatively simple products with only one kind of metal needed for each recipe, so it makes sense for a foundry to cast/extrude these kinds of things.
Engine units, inserters will be added to the gravity assembler when I make it able to support the space age mod (recipe and surface condition, etc.). Don't have time yet, next week maybe.
