I wasn't aware of this conversion kit until just now. It's a good idea, but I haven't tried it or seen it in person to be able to offer much advice as to how it works. Generally, I wouldn't recommend oversized bars with IHC as people usually try to do this with multiple shims, which creates instability. This conversion kit may work, but I'd be skeptical until I see it working in person.
Nope, an SCS won't work as a clamp for HIC because it has a ledge inside the clamp and 2 different different inner diameters for bars and fork. If you need a taller clamp for HIC, look for an oversized triple or quad clamp. However, your clamp should only need to be about 2 inches tall, the same as the slit in your bars.
If you have an external clamping mechanism (ICS, IHC, HIC), then you need a slit in your bars. Without the slit, the bars will resist compression and the clamp will do nothing to squeeze the bars against the fork or shim. The slit allows for compression of the bars. This is not true with SCS as you want the bars to be solid and resist compression since there is nothing inside the bars.