No thats not the way to do it. Remove the nut. Find out its thread and tap a bit of 1" long 3/4" rod to this thread. Cross drill your new nut at a point higher then the bit of thread sticking through the tailstock. Screw your nut on and see where the hole lines up with respect to the casting. Now to lock the tailstock, the hole must be behind the front bit of the casting. So you can add washers to suit or if you are ambitious, turn a bit of the actual thread end. A washer is required anyway. If its not fitted fit, a strong spring between the clamp and the underneath of the tailstock.
If you have succeeded, putting a bar through your cross hole and pulling it should lock the tailstock, pushing the bar away will unlock the tailstock. The spring it to push the clamp of the bed as it has a habit of freezing to the bed.
Myfords for all their years in the trade never thought of this either !!
Frank