As chicks, the sex links are pretty much all black (unless it's a boy, then there's a white spot on the head) and austrolorp chicks have quite a bit of white/yellow on their heads and chest. As adults, the sex link hens feathers are black with some iridescent green, and some red feathering around the neck. The austrolorp's are all blace with the iridescent green. no red around the neck.
Yeah, as chicks, a lot of black birds look similar. If it has a spot on it's head, it's a sexlink, or possibly BR. If not, your guess is as agood as mine!! I had two pullets that I thought were sex links as day old chicks, I posted a thread on here for peoples opinons, some people said Australorp, most said sex link.......
Now that they are a month old, they don't look like sex links anymore, one still may possibly be an australorp, and the other is a possible Jersey Giant. Sorry I'm not much help, but I think it's a waiting game on young black chicks, unless you're a pro.
I also have one with red eyes! And I have 2 that have a lot of red feathering now that they are fully feathered, one has a minimal amount, and the fourth one is nearly all black with a lot of shimmery green feathers. Maybe it just varies? I know my golden comets are all different--some are more white, some are nearly solid orange/red, some have almost lacing patterns on them, etc.