Any time you're trying to move rubber(or plastic) against metal, just spray a mixture of water/rubbing alcohol on the surfaces. Some inside the hose, some on the neck in this case. It will slip right on, the alcohol will evaporate and leave no residue. If you have it half way, slip a small shafted screwdriver in between the hose and neck and squirt some mixture in there. Then grab a channel lock pliers and work the hose back and forth in a slight twisting motion while also pulling toward the radiator. Should go on rather easy.
I use the alky trick any time I'm running wires through an insulating tube, literally any time I want something to move smoothly through a tight space. I used it in great quantities when changing the plug wires for new and used the OEM boots. Wires came out and the new back in slick as greased owl....well, you get the idea.

It's something my grandad showed me over 60 years ago and I never forgot it.