Crow
Crow Person
Yeah the blades have an interesting story. The guy I bought them off lived in a village called Overton, just down the road from Horbury - where his dad worked at the Slazenger factory.
He apparently was given the clubs to go and use, to test them out. If the clubs were deemed satisfactory then they’d be produced and stamped with the required branding. Seems plausible and from a quick search they do look similar to these below.
He would have had a full set originally but the guy was explaining how his dad split the set in half to share between him and his brother.
That model of Ballesteros was a lower price set and I doubt they'd have gone to the trouble to make a prototype, it isn't quite the same profile either, see below.
This Slazenger Plus International from around 1972 is similar and looks a more likely candidate.