Thanks Michael, these are measuring between 5.82 and 5.85 which may explain the slackness. Next week I'll nip in to Don's again and bend his ear further. Hacksawing & filing I can manage. I think hack is the operative word here. I suppose I could make up a little jig and do the head profiling with a bench grinder and/or belt sander. NOT angle grinder.
Nick.