Yes, Race Tech said the check plate and spring options. I was guessing it might be just springs also but I guess that's kind of cynical. I don't like the idea of paying an extra $60 to select the proper spring and asked the amazon seller if his plain 3301's come with three sets of springs like the S-3301's come with …
There are two springs. A small one that governs the internal washer (check plate) and a large one on the outside that allows the top to "blow off" on square edged bumps. I doubt if there is anything different than the springs and I also doubt there is any major change on the check plate spring that you couldn't overcome by using a lighter weight oil and adjusting the top spring.. of course that would affect rebound too so unless you have the adjustable 1100E forks like me you might have to play around with the springs.
This is worth a read if you haven't...
https://racetech.com/page/title/Emulators-How They Work
In my KLR I use a Ricor set, they actually have a serious of small washers inside like a full cartridge does.