I've done the late hunt in 505 and found elk, but had a tough time putting it all together. The elk aren't everywhere in those units so you will need to find where they are hanging out and if that is public/accessible land. Also there is plenty of pressure so after the first day or 2 the elk are usually pushed away from easily accessible areas to places where lots of walking is required and also in small groups of just a few animals. If you can scout this week in 505/503 and find something, or give it a go the first few days, but if you don't find anything soon I would stick to an area you know better if you want some meat for the freezer.