Cost of acquisition of Long term capital Gain & investment us 54EC

If a person has one very old flat thereafter a builder gave him one new flat in consideration to old flat. I think this transaction will attract capital gain. But the assessee has not filed ITR for that year (Even if he would hv filed ITR for that year then there would be no tax because of section 54 exemption I guess). Now he sold that new flat also after 3 years for say around 60 lacs. can he take the FMV of this flat as on the date of purchase as its cost of acquisition & balnce amount can be invested us 54EC ? or shall he invest entire 60 lacs i.e. after taking COA as Nil?? plz advice on this matter ( Expecting the reply of Dhirajlal Sir)