Unless Rotax have changed it, the elbows into the water pump take Loctite 243, while the elbows into the heads take Loctite 480.
I repositioned the elbows into the water pump using a dowel and a propane torch, as you describe. But I did it with that part of the water pump off the engine and held lightly in the soft jaws of the vice. It felt a bit amateurish, but it worked.
Due to an error not of my making, I ended up having to replace one of the elbows on the underside of the heads......and that wasn't easy. As I recall, I ended up using acetone and one of those gun cleaning brushes to clean out the threads in the head.
As noted, those elbow threads are very fine......and they are also 'soft as butter'.