The baseboard (or rather projection board in this type of construction) can be taken off for groundprojection as Durst stated. This would mean that the barrel thread enables enough rise of the lens for focusing.

I rather would advise for gaining larger than baseboard-size enlargements to lay the enlarger horizontally an the table and projecting to a wall, thus yielding a variety of scales, in contrast to the single one dictated by the height of the table when projecting vertically.