if only lowering the subframe to do the wishbone bushes then i'd undo the rack from the column from the single bolt at the base of the column inside the car. this way you wont need to worry about dropping the subframe a bit with the t.r.e's still all connected and the whole lot can move as one.
you can try giving the bolts a good spray, and also have new bolts to replace them with as the originals rot away inside the hole and lose alot of strength.
youll need m10 x 30 or 35 for the rear mounts, and m8 x 25 for the front mounts. try and get high tensile 12:9 bolts, ideally zinc plated.