I do believe "until extended" worked! I selected the hidden face of the inner/finished model as the object for "until extended" and the body of the visible/cast model as the body for the extrusion, and it worked; thanks! I'll keep plugging and see if it continues to work.
-WRM
Oh, and yes, I kept getting errors with the other end limit selections.
-WRM
Oh, and yes, I kept getting errors with the other end limit selections.