repechage

I hope he is joking.

I am not fond of that stem anyway, but I think some investigation is needed before you go whacking things.

Some of these bikes had a Wood dowel in the steerer base, if it does, use a small diameter rod and check for depth blockages. Test, don't guess. I would also try inserting the stem without the expander hardware after things are looked at.
Reynolds steerer's of the period had tapered wall sections, there is always a chance the taper starts too soon.