How do I remove undercoating?

[CamarosRus]

I'm still cleaning bottom of this Norwood 73 Camaro body. All the undercoat is long gone.
Spending way too much time trying to get clean enough (??) so as my SPI Epoxy primer
will have good adhesion.
Curious IF anybody reading this has cleaned under floors of a resto project that wasnt
being sandblasted.
Knowing what I do know, I wouldnt recommend that anybody do it THIS way...

Media Blasting is only way, best way....but my sandblasting vendor wouldnt blast undercoating as his media (sand) would then become contaminated....
After I removed undercoat he then quoted me $400 to blast off bottom, which I probably should have done......but figured Id just finish the cleaning myself................