Add the remaining 2 tablespoons of canola oil to the skillet and heat until shimmering. Add the tofu, garlic, shallot and preserved radish and stir-fry over high heat, until the garlic and shallot are golden, about 1 minute. Add the noodles and 3 tablespoons of the tamarind sauce and stir-fry until the noodles are coated and most of the sauce is absorbed, about 2 minutes. Add the egg and chives and cook, stirring and tossing, until the egg is cooked, about 1 minute. Remove the skillet from the heat and stir in the peanuts and dried shrimp. Transfer to a plate, top with the head-on shrimp and garnish with the bean sprouts and lime wedges. Save the remaining tamarind sauce for subsequent batches.