I'm moving this post to something more descriptive of the thread in the hopes it helps the next poor sap who wants to import a Sub 2000 into California.
Yes, the Sub 2000 needs two modifications to make it legal. It has to have an over-all length of 30 inches and has to have either a bullet button OR a monsterman grip.
The length thing is pretty easy to accomplish by either installing the stock extension (good luck finding one) or slapping on a recoil pad -- as long as it adds more than 1/2" in length. Apparently the extension doesn't have to be permanently affixed. The bullet button installs in about 5 minutes.
To get the thing to California, you can do one of three things:
1) Have the modifications made out of state and shipped to an FFL in its California-legal configuration.
2) Have the un-modified version shipped to a Class 7 FFL here in California and have them modify the rifle.
3) When I was looking at building an AR-15 instead of the Sub 2000, I didn't run into this problem. A lower receiver can be shipped into California without modification. An upper receiver can be shipped into California without modification. But if you put the two together, that's a big no-no.
It would be possible to ship a disassembled Sub 2000 into California legally. I'm not sure what level of diss-assembly would be required, but taking the rifle apart at the hinge seems the simplest route. The receiver would have to be shipped to an FFL (unmodified), but the barrel assembly should be able to be shipped directly to your home.
Hope this helps any other poor saps who live in California and want a Sub 2000.