I had a more extensive surgery, and the same IMRT radiaiton as your Dad.

I can't say that I had a salty lingering taste in my mouth particularily. It's taken a long while for my taste to be anywhere close to normal. I have days where nothing tastes right, and my tongue is so sensitive that even water that isn't cold enough tastes really funny.

I find that I brush my teeth 5 or times a day, and that tends to keep the odd tastes under control. A mild toothpaste is a must for me, though. Something strong just substitutes one overpowering taste for another.

The dry mouth is something I think we can all relate to. Most of the products you mention give very short term relief. A water bottle has become an extension of my arm, almost all the time. There are a couple of drugs available that may improve the level of salivary function for him; one is salgen...you may want to talk to his doctor about it.
Wayne