I've roasted larger birds using the Zuni method. I've had the dish at the restaurant and used a 2.5 lb bird the first time I cooked a Zuni chicken, in order to establish a base line. It definitely tastes better with a smaller bird, but birds under 3 lbs are really hard to fine, which is why I end up using larger birds.
When cooking a larger bird, definitely go the full 3 days. I've gone as far as 4 days. Even for the 2.5 lb bird, I brined it for 3 days, per the Zuni recipe.
I'm interested to see responses to this, since the Zuni recipe specifically recommends using a smaller than average chicken (IIRC, about 2 to 2.5 pounds?). I think it's to do with the hotter but quicker cooking times - if you roast a chicken at higher temperatures for longer than it takes to roast a small chicken, you might dry out the white meat before the inner dark meat is properly cooked. That said, I think it's definitely worth experimenting. I think some people on this board have even Zuni'd a turkey!
In terms of salting it, I would give it longer than the one day minimum. For smaller chickens, I often leave them for three days, and they don't seem to get too salty. Not sure how much longer than that you'd like to leave a raw chicken in your fridge! Interestingly, haven't noticed much difference in a chicken salted for 24 hours versus three days, although perhaps this calls for a side by side taste testing - both seem pretty well seasoned. So I'd salt it and leave it for 2-3 days if I were you, just to be sure.
Please report back and let us know how it goes.