Removing undercoating?

[Bob D]

I finally got my cab off of the frame today. Not easy to do alone with only a bottle jack and some scrap lumber. Now that I have the cab on its back I see that several of the PO's had coated the underside with every imaginable goop to prevent rust. Also found some seam sealer holding on cab supports and white kitchen and bath caulk sealing the back of the rockers.
Is there any trick to removing the tar-like stuff? Some is still pliable, and some is very textured and hard as a rock.

Bob