I reeded two of these (of slightly later vintage) last year with some success, but frustratingly I cannot find my notes on them.
I would not make the head wider than 11.0 mm, perhaps 10.5 to start. I recall the scrape being a bit shorter than I would normally use - if memory serves it was 20mm or less - the “head speed” seemed to need to be relatively high. I believe I used one of my standard flat staples, which would be slightly tapered from about 3.3 to 3.5 mm I.D. over 50 mm - I am pretty sure I shortened the staple to 47 or less. I don’t recall if I ended up rushing the staple down smaller or not. My narrow-bore reeds tend to hover around 76-78mm, but these may have been shorter. They were almost certainly not longer.
If you remain stuck, PM me and I’ll try to retrieve one of the spares and measure it.