you just cant pay duty for the body change. here what will certainly happen to you.
You will get change the body of 1993-4-5-6-7 body to your chasis by paying xxlacs rupees, then after doing that you will be driving your car with 10 or 12 years old number plate, then suddenly one day your car will be lifted by FIA or Custom Intel of IB or any other agency (which are very very active now days) your car will go to court custody after completion of the case your car will be Auctioned in a Govt Auction.
In simple words do not convert your car body with newer model or else your car will be gone all together, instead add some more money to the program and buy an auctioned vehicle with clear title.