I feel like up the line bidding and playing 1c-1d-1h-1s as 4th suit game forcing are incompatible. With most my partners I play 1s as 1 round force, but not to game, that can be sorted out later. With up-the-line I kind of feel it's mandatory to play this way.
Especially here with GIB a passed hand I think it can bid 1s naturally. Opener besides 4423 could also be 4414/4405.