I don't know if you want to sandblast the interior of your car... I helped my brother do that to his 1965 plymouth valiant a couple summers ago, and unless you plan on literally removing every part in the inside of your car, it's not worth it, buy a power sander.... there is STILL sand coming out of weird spots in that car when you drive down the road..
and oh yeah, that tar stuff on the floorboards of factory subes is horrible... I had the best luck with a 3/4" grinder with a bigass wire wheel to get it out of my xt6