Gromit (C15) back in the fold but with faulty Left Hand Footrest Stud

[Gromit C15]

My BSA 1960 C15 (Gromit) has just returned after Rebore, gearbox work, and new Amal carb (376) as the fitted head is SS80 spec and the previous one (375)  was for original head. Unfortunately the Left Hand Footrest Stud is now showing its age and needs replacing (see photos) I have ordered new stud, anyone have advice on easiest way to take off old one and refit replacement?

[Rupert]

 Looks like it's scrap so weld a steel bar onto it and unscrew it.

[scifi]

It's been a long time since I saw the workings of a C15 footrest, but should it not have either a square or star shaped location, to hold the footrest in the right place relative to the brake pedal..?   Is that welding a chewed up locator.?

[V500]

As I recall it's a spline. Looks like the remains of it on the left of that horrible stud.