Mild steel means low carbon. Definitely cast. More likely to bend and break.
EDIT: BTW...if we're going to start casting something for these trucks...why aren't we doing the trim rings for the 3/4T Spicer lockouts. No safety issue there (though I assume no one is hooking a chain the those repro hooks), and IMO there is a definite market for them. I mean the repro plastic dials are $100 for gosh sakes.
DOUBLE EDIT: I guess these are stronger than I would have imagined according to 72ironmike:
https://67-72chevytrucks.com/vboard/...d.php?t=818316, but GM forged the originals for a reason.