cst and sad set off in gst on closing stock on 30,06,17

dear sir

we are registered dealer and importer who buying polymer from ongc govt co and other registered dealer of different state by paying excise n cvd , sad and cst on material.

my question in gst can we get set off of all three excise/cvd, sad and cst on our closing stock with us on 30.06.17 which we bought in previous months before starting date of gst ie 01.07.17.

what will be the procedure of such set off claim and what will be set of against what in gst.

pl help....