ahh
so you're planning towards trying to remove the UC and leave the under finish unharmed.
And probably laying on your back under the car jacked up on big stands. I've done undersides that way - but they didn't have any UCoat. And we painted them.
You'll probably get sick and die doing all that. j/K
Its a good thing your 2 wives live in seperate levels of your house.
I've used odorless mineral spirits for years as a grunge cleaner and degreaser.
It works great... and its OdorLess (gift from God). It will dry out your skin a bit after prolonged exposure. (gloves)
If it will work on that UCoat in beginning, mid or final stages - it won't pull off any factory finish. And you won't get further drain bamage from over exposure trapped in a basement full of fumes.
If its held up decent all theses years, its probably a good enough product that its also chemical resistant by design as well. The crappy stuff would be flaking off in lots of places by now.
Window ice scrapers, wooden paddles, plastic razor blades in a razor scraper, etc.. will be good tools after you find out what softens it the best for you.
Too bad you can't turn car upside down and let saturated rags soften it.
jimwangers has an old trick for that
Best luck to you Man