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AD768 noise

I am looking at the AD768 for the simultaneous generation of 64 high purity carriers between 1-10 MHz for a space application. The AD768 is old but that is the only space-rated >25 MHz 16-bit DAC with low noise that I have identified.

Can anybody know if the output noise mechanism of the AD768 is fundamentally a current noise, i.e. does it scales linearly with the output impedance? In some mode of operation I want to scale down  reference current to 1 mA and I wonder if other sources will start to dominate.

Also on the subject of noise, has anybody performed a SPICE simulation of a DAC output noise, most specifically the 1/f noise (I do not worry about the quantization noise)? Is there a SPICE model I could use to simulate the effect of that noise? If I were to build a simple output model  (e.g. bipolar switching transistor on a R-2R ladder), what kind of simple circuit should I use?

Thanks for any comments and suggestions,