Thanks dj,

yep I used a brass screw and washer. The new coil was specified from the parts manual, which agreed with the little bit of cardboard (you can just see in the picture) stapled on the location of the coil in the headbox. It used a smaller attachment screw, which was inconvenient, but the coil was physically the same size.  Electrically it measured the same as the other functional units of this type in the game, 10 ohms coil resistance.

I have now tracked the fault down to a relay contact not operating properly due to poor adjustment and this explains the failed coil in the machine as I purchased it.  It was right up the back of the cab and hard to see, so I removed the pf and did a bit of cleaning vacuuming and went through and cleaned / checked / adjusted all contacts.

Now just about everything on the game is working and it's quite a fun player. I'll post some final pics when it is all set up.