Interior rivet size for 1949 Liner

As mentioned in a previous thread, most of the interior skins were held in place via sheet metal screws. However, the semi-spherical upper skins (is there a term for these?) at either end are also attached by rivets. Does anybody know the type (blind vs. solid) and size? I will need to drill them out and want to make sure I'm using the correct bits so as not to unduly enlarge the holes or otherwise damage the skins.