Unless I'm mistaken, I think new chainrings are still 3/32". Isn't it the plates that are thinner on 9-10-11 speed chains, rather than the gap between the plates? Modern chainrings have all manner of ramps and funny shaped teeth to aid shifting, but I don't think the teeth are any thinner over all. You could try placing the chain in question over the chainring teeth to see how it feels.
Disclaimer: I haven't personally tried running a 9sp chain on old S.Record rings.
Nick