Information on hoppers and model info?

[NW Modeling List]

I got pictures of several of the 17XXXX series Covered Hoppers yesterday down
here in South Carolina.
 
http://www.rrmodel.info/2010/09/norfolk-western-in-south-carolina-2010.html
 
Couple of questions:
 
When would this series been built?
 
I noticed that they are marked "Grain loading only" but they also are displaying
hazard placards? Any idea what they are carrying?
 

>From the modeling side:

 
Are there N-Scale versions of these available?
 
Thanks in adavance...

Gene Bowker http://genebowker.com/
The Railroad Examiner - http://railfan.biz