Typically you do Ground school for the 300 efis model and then Sim of 8/9 sessions on the same. A short differences course and a couple of extra sims on the 700 or 800 gives you from 3/4/5/6/7/8/900 on your licence. Base Training is usually done on the 300 and you should not have to repeat it for the NG.
Interestingly, here at Astraeus Towers, we are just about to start NG only type ratings at customer's request.
If you show up and want to buy a rating however, it will initially be the 300 efis. Hope this helps.