The book beta on narrows says easy class III. Higher water is IV- and I think it mensions portages and scouts are possible pretty much everywhere. In terms of remoteness and comittment you are right in a slot canyon, game on. Don't think it wise to go on this one alone while probing your first decent!
I have never done the slot, but by late april I think I will have at least once. If not I will be up for the run by then. Send me a message in late April and wife and I will probe it for you!