Don´t believe they were ever used by Jensen...but will be happy to stand corrected.
Personally, i´ve always considered those empty pulley shafts, a leftover from the H.Lange original design, as they always had a pulley on there.
Come to think of it, i do not believe that i´ve ever seen a Jensen drillpress, with an original pulley fitted on there.
I just noticed that on the Jensen #200 Workshop "the Jensen that was never made" , it has a pully down on the bottom and and is used in that picture.