Third parties still involved in these low volume turbos? How do they pronounce aluminium in Qld too, or was a US education involved?☺️
Hard to tell how deep the first defect is. When making bellmouths in the past, toolmarks were erased with a quick pass with paper, might be a bit of a trick to get between those lips! Perhaps a thin stick with some fine emery might have fixed that first housing. I'd probably worry more about abrasive grit getting past aftermarket air filters than those tiny bits though.
I'd think with likely flood coolant on a small production run, rather than a 1 or 2 off, and css, there's not going to be a huge amount of heat at the insert cutting this stuff.
I see all the multiple drilled and tapped holes on the BW housings, doesn't strike me as a good idea to use non heat treated material, even if it does save a few cents. The B1 frame ones I've glanced at, do seem to have that fine grain usually associated with hardening of 356, although sometimes the deeper you go into a casting or even wrought bar, the gummy bits appear.