In case anyone stumbles upon this thread, here’s an update. The sheave assembly in question has been removed and shown below. I guess I have a snowball’s chance in hell of finding a replacement….
[attachment=0:337ddtaz]tony boat 002.jpg[/attachment:337ddtaz]
[attachment=1:337ddtaz]tony boat 001.jpg[/attachment:337ddtaz]
Big thanks to Colin who put me on to how to remove it. The assembly was punched out (it wasn’t easy but it worked) from the aft of the mast, through the mainsail luff channel. As I’ve been told, the 2nd sheave must have been for a 2:1 reduction pulley system that would have originally been used to tension the jib halyard. The mast has clearly been modified.
Looks like I’m back on the water, but am defo on the lookout for a 2nd hand mast now.
cheers all and thanks for the help.