My exterior whitewash receipe is simply white portland and lime mixed evenly pound for pound. My only concern is that I am applying it to new unprimed stucco. Any suggestions would be appreciated.

use it as it's own primer there is no need to prime the stucco with anything else. your situation is quite ideal.

Well, you should be punished to call the mixture op cement and lime "whitewash"!
This mixture will be to hard, will not be damp-open, the wall will not be able to breath nor to sweat in a healthy way. Contrarary to a real whitewas, which is made with lime. For exterior purpose you might add some caseïne.
But no cement.

> For
>exterior purpose you might add some caseïne.

Lime will "eat" casein just like any other organic stuff.
Cement is in the stacco to begin with, adding it to lime wash will not hurt, just think about it...