Oversized bars are made for either HIC of SCS compression. If you clamp them enough, they'll fit threaded compression, but they'll be crooked, and you'll notice that they're crooked when you spin your bars stationary. My bars are kinda like that.
Also, HIC will work with a threaded fork (although it's pointless unless the only bars that you have are oversized and you don't want to buy a new fork). Just put a star nut in the fork and put the shim on it. You'll need a new headset though if you don't already have a thread-less one.
Also, If you put them in SCS, then you will need to get rid of the slit. Depending on how deep you cut the slit, you can just cut 2 inches off the bottom of your bars and hopefully it'll get rid of 90% of the slit or more. Then your bars will be the same height as before once you put them in SCS. If you still have a decent sized slit once you cut 2 inches off, you can find some tubing to use as a shim to stick into your bars.
I'm hoping I answered all your questions.