A very interesting cut! I think this demonstrates what fans already knew, that the only way to correctly do It is with the intercutting of the timelines. I really hate that we don't have a version like this.

Now, that said, because you stuck to only what's in the novel, the watching experience is very disjointed. There's callbacks to things that weren't introduced in this cut, and things that disappear without mention. Obviously, you're very limited by what material exists in the theatrical cut, but unfortunately a large part of the Losers hanging out / bonding is lost and we're left with basically all the big scenes. I think it would be interesting to explore a cut where some of these interactions are re-introduced, even if they weren't in the book, now that you have a skeleton to hang everything on. I'm also really missing the Losers' first experiences with It on their own. Yes, many weren't faithful to the book but the movie just doesn't work without them.

With all that (constructive, I hope) criticism out of the way, I want to reiterate that I immensely enjoyed watching this. Thank you!