Section 54

Hi, I recently sold my residential flat for 78 Lacs (which is higher than stamp duty value, therefore sec. 50C not applicable) , which I purchased 3.5 years ago for40 lacs. The Indexed cost of acquisition comes to58 Lacs, which arises a long term capital gain of 20 lacs (78-58)....   However, 2 months ago(from the date of selling above flat), I had booked an under construction residential flat from a reputed builder for 70 lacs, the possession of which is after 3.5 years. I already paid 25 lacs as down payment, The rest of amount will be paid in installments(which fall after this prev. year) as and when the due dates come up, I have availed credit facilities for the payment of above installments.   Am I eligible for exemption u/s 54 of the Income Tax Act? If yes, Any comments/suggestions would be highly appriciated..