Tar-like undercoating on 63 Valiant...any way to remove it?

On my 1964 and 65 A's, I just pried off loose chunks under the floors, which was just a few spots which likely took impacts from road debris. Those areas had light surface rust underneath. Where I pried off secure undercoating, the metal was shiny and the undercoating well-bonded, so just left the rest on. Same on the splash shields in the front wheel wells (worked off-car). I only removed all undercoating around the UCA pivots (mostly loose so came off easy) and the lips of the fenders where I used a wire-brush (undercoat makes fine rubbery "dust"). I cleaned and painted the UCA's off-car and installed Moog offset bushings for more caster (different than instruction sheet).