So, if I'm correct, the longest combo (excluding the special) is 280. Because a hit from the special does half damage you can technically hit an enemy 20 times if you're really lucky.
Doing a headsaw finisher does 2 hits so normally, you can hit an enemy 9 times and if your next attack is headsaw, then you can grab and attack and it does a headsaw finisher.
So, if your really lucky, you might me able to get 350.