The helical means the teeth are not straight but curved. Only the pro kits come with helical gears what Caster call version 3 gears your kit comes with version 2.
You can see on the link the curve on the teeth
http://casterracingusa.com/product.p...1&cat=6&page=9
the engine mount you are going for looks awesome.
Have you ordered it? The only thing i have noticed is it is wider than the standard caster one and will move the motor forward slightly which is the only thing putting me off getting one which is a shame because the standard caster one is poo.
Are you doing the weekends racing at Nene 20-21st August?