Excellent question!
I've been looking into this for my FWD buggy, and have documented the information in topic on oOple. I think you're looking for the following topic:
Long vs. kit outdrives
The outdrives are 1.25mm longer (per side). It doesn't sound like much, But I found it very useful on my FWD Buggy. Probably more relevant for you, I found it crucial on my DEX210 to keep my driveshafts safely seated inside the outdrives (especially as I did a few small mods to enable more droop (limited on the shock, not on the chassis). I can't understand they put these outdrives in the later batches of 210 kits as standard, but at least they exist
Also worth noting by the way: The gear diff outdrives are already longer than the kit ball diff ones which put the diff at the same width as the ball diff with the long outdrives.