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Definately the Vine Hawk moth (green form): http://lepidoptera.butterflyhouse.com.au...
By imitation grape vine, do you mean a fake (plastic or silk) one? That would be pretty funny since it uses real grape vine as a host plant.
I see that Hippotion & Sphinx are synonymous.
I'd say it's a sphinx moth larva. They always have a large horn at the tip of their abdomen and no hairs.