Very ambitious target, but one sure way to get great results with Cambridge weight plan is to stick to it 100%
I won't say "Yes it is possible" it just wouldn't be fair to raise your hopes that high, but even if you manage 5 stone in those 5 months, you will be well on your way. You will feel better about yourself, and in turn IMO feeling better is a huge step towards looking better.
Good luck with it.........I look forward to hearing of your results