Pretty sure GM used nylon on g-bodies still, it wasn't metal asaik. GM and Ford, maybe Chrysler but i'm not 100% sure, used plastic tooth aluminum gear they claimed to make less noise. About 80k miles later the teeth come off, pretty well known and some people noticed an afro of particles on their drainplug magnet using aftermarket metal gears so went back to OEM plastic tooth gear. IMO metal gear is better but I use a magnetic drain plug and it does grow an afro. Billet gear might not do this.
If you do come across the OEM plastic gear that has lost it's teeth, it's a good idea to have a look at the oil pump pickup screen, it might have bits of teeth clogging the screen.
I have always used good quality true roller double rollers and I know now the stuff I run is all billet but the ones I ran years ago I wouldn't be sure but either way I never had an issue with metal shavings..
IMO using a nylon toothed sprocket is just adding a point of failure that is completely unnecessary.
Yes, many people do upgrade to double roller but those scare me a little. Call me weird maybe, I'm more comfortable with the durability of link-belt style chain b/c I've never seen one fail. It's comforting to learn my 81 305 might not have the nylon gear, I haven't been in there yet. My '69 Chevelle 350 did have the nylon gear. Perhaps the metal particles from an aftermarket sprocket aren't a problem, probably not is my guess, just saying the magnet picks up an afro that didn't appear with the plastic gear.
When it doesn't appear with a nylon gear but does appear after changing over to metal aftermarket. Perhaps this is only temporary or tapers as the sprocket is run over time, the afro growth does seem to slow to some degree.
I prefer to use the magnetic drain plug and this is one example of why, that's just me I suppose?