And it wasn't just the Spad & OV10 that were impacted by the rapid proliferation of MANPADs; Israeli FJ aircrew received a nasty shock, as did fast movers at low level, and helicopters, over SEA. Let alone the Sovs in Afghanistan....
Since the introduction of the Strela (and it's progeny) IR DAS has become a top priority for low flying ac -esp RW and CAS platforms, and, using a combination of suppression, jamming, detection, decoys and tactics they can be dealt with. There is no reason at all why new-build OV10s wouldn't benefit from these advances and thus be more survivable in the low 'n slow environment.