I was in exactly the same situation and I used the below in 2 x 70.3s in June. Worked great with the spacer provided between the fabric saddle bosses and the mount. Disclaimer! . . . It did unfortunately all fall off during the 2nd race after some bumpy road but I didn't think about re-tightening prior to that 2nd race, I don't think it was a failure of the mount itself but just worked it's way loose so if you go for it something to remember! . . .

https://www.amazon.com/...00?ie=UTF8&psc=1

I have the same Saddle and just run a single bottle in the back and the profile design BTA bottle up front. Honestly for a 70.3 you won't need much more because you get bottle exchange. I run a double serving of Infinit in a 1 Liter bottle BTS then just grab water for BTA hydration up front at every exchange. My biggest problem comes on training rides where I don't get bottle exchange. I add a cage to my downtube for those.

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https://www.strava.com/athletes/23685202

I've been running exactly this setup for a few years - works well, mine hasn't so far fallen off either !!