1) I hope you are aware Zipp rims are fitted with oval rim washers, that need to be removed and replaced with new (non deformed) ones... it is a royal PITA
2) Sapim CX Ray is already a flimsy spoke, I would not use anything lighter... too fragile to handle and will most likely fail quite rapidly and will have lower stiffness.
3) For a bit of advice, this is my rebuild of a 303 on a Dura Ace hub, if that helps
whosatthewheel.com/2014/12/27/zipp-188-hub-and-a-firecrest-rebuild/
Last sentence:
if you can’t find the odd length, round up, as I did.
Couple of points
1) I hope you are aware Zipp rims are fitted with oval rim washers, that need to be removed and replaced with new (non deformed) ones... it is a royal PITA
2) Sapim CX Ray is already a flimsy spoke, I would not use anything lighter... too fragile to handle and will most likely fail quite rapidly and will have lower stiffness.
3) For a bit of advice, this is my rebuild of a 303 on a Dura Ace hub, if that helps
http://whosatthewheel.com/2014/12/27/zipp-188-hub-and-a-firecrest-rebuild/