Voile has 3 size kits available; Short Rod, Std Rod and Women's. Unfortunately their sizing chart assumes that the kit will be used with the Voile toe plate and may therefore not be appropriate for use with the Zero Pro bindings.

My best estimate of the appropriate Voile Switchback Backcountry Kit for use with stock Zero Pro bindings is:
Short Rod: 290 to 345 mm boot sole length
Standard Rod: 325 to 380 mm boot sole length

The link to purchase the kit is: http://www.voile-usa.com/Merchant2/m...roduct_Count=8