I dont think it's daft at all, Bob.
If you look at the clarke major mill or older tiawanese Ajax milling machine, this is basically an inspired step up from a pillar drill,
They kept the round column, and fitted a dovetailed compound table and fitted a rack and pinion movement to the head.
Later on, as we can see there are many more mills around now which are built from the ground up with dovetailed head too.
You just have to be careful with the quilll, not to use it extended and setting the depth would be rather iritating after a while. I would consider getting a proper one, would be my advice though, it would be a whole lot of trouble to get it to a user friendly state.
Michael W