Yes, the mounting of the engine, main supporting angle iron (so-called the part of the chessie) needs to be altered a bit if the diesel engine manufactured by the same company (toyota in ur case), for the same model (parado) in your case. If you are using a 2700cc Parado petrol engine, then its very much possible to use a 4000cc (Parado)diesel engine without any main alteration of the chassie.