Roos will grow their crest feathers back when they begin to feather up, while most hens will grow their crests 'up'. The roo's crest will look spikey and the hen's will look poofy.
Combs aren't visible so you must look for redness around the eyes and face area...also keep a look out for wattles that will develop on roos quicker. Hens don't tend to grow wattles until they are close to laying time, and the breed are very late layers. (Mine started up at around 9 months.)
Watch the tails. Roos will, as expected, grow them flow-ier (sp?) and hens will keep them up. Then just look for typical roo stuff and behavior. Crest sexing is misleading. I wouldn't recommend it.