Great idea. Have you considered the plastic grinding tools/brushes from 3M. They are much nicer than the wire type. I have been using them on the underbody and like you they produce a bunch of little bits for the shopvac to pick up. I agree that not overheating the tar is important. We also used a paint scraper with chisel edge and a hammer-very fast.

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Grandpa's toys-modded suspensions and a few other tweaks
'89 CRX Si-SCCA ITA #99
'99 Prelude=a sweet song
'03 Dodge Dakota Club Cab V8-Patriot Blue gonna tow