IMHO, after the excess is removed with SHARP small chisels, machinists' stones, in varying degrees of coarsness, is the way to go. Keep the area well flooded with varsol to greatly cut down on the loading of the stones which Ellis refers to. Shape the tips of the stones to the needed angles, either on a grinding wheel or on a large, coarse, sharpening stone. Wet-or-dry paper, folded over a backer, just can't get into the tight corners as well as a stone does, by virtue of the thickness of the paper.