Masthead rig modification.

[Jill]

I wish to convert my rig to a cutter. It is currently the standard Victoria 7/8 rig.
Has anyone done this? My main concern is modifying the masthead for attaching the headstay and installing a sheave first the halyard.
Any photos of either the “standard“ Proctor masthead, or better yet, a masthead rig mast head would be most helpful.