Hii aspirant , 

Coming to your question I would like to tell you that you can get cs but not in the good nit at this percentile you can get till the last round in the north east nits even if the cs seat remains vacant till that time and yes there will be a requirement of your OBC NCL certificate as it is one of the most important document which will be checked during the document verification, to get a cs in the 3rd round is impossible you can get into the last round maybe and that too in some gfti .

Hope this helps you , 

Good luck.