Capital gain sec 50c

hi friends, (the transfer of property occured in f.y 2008-09) Mr.A sold a Land to Mr.B for a sale consideration of Rs.20 lakhs(Stamp duty value :10 lakhs) Indexed Cost of acqusition: 3 Lakhs Mr.A invested Rs.7 lakhs in capital gains bonds & he paid long term capital gain on remaining 10Lakhs @ 20% But Mr.B prepared the sale deed as per stamp duty value i.e Rs.10 lakhs and paid stamp duty as per Rs.10 lakhs Now my question is whether showing of the excess amount Rs.10 lakh (20lakh-10 lakh) under the head capital gains in income tax return is correct or not for which no other sale deed is available