I do not believe that you can switch the screens across the different models. By doing that repair, you could possibly be compromising the integrity of the water-resistance of the watch. It definitely would be interesting if it was possible.
In regards to the screens being available, they shouldn't be available form iFixit for at least another month. I am sure, though, that they are working as fast as they can to get the products to market for purchase.
Hope this answers your questions.