Unless you're lost wax casting, you're going to have to cast a lug as a solid lump then drill and bore all the internal cavities out afterwards. Even with lost wax casting, your going to have to bore the tube holes to size. And I imagine making a jig to hold a lug casting at the appropriate angle will be a complex job in itself. You also need to factor in going though a few iterations to work out what shrinkage factor you need as a casting will not come out the same size as your mould.
I was thinking that lost wax casting would be the way to go. Or in this case lost PLA. People who have been experimenting with it say that the shrinkage is actually the easiest thing to deal with. Once you've drawn the shape you want on your CAD program you simply use a scale up function to increase all the dimensions 3% (for Aluminium).