UPDATE, 5 Sept 2016
I now have some slightly better, and significantly larger, images (click each image to see the large versions):
It no longer looks as if John has a large halo, but it is clear the Christ does have one.
The Cross is 'T'-shaped.
Mary is wearing a veil and has her hand to her cheek.
John appears to have his hands clasped in front of his chest.
A skull is clearly visible at the foot of the Cross.
There is a coiling acanthus border around the image.
The blurry images above are variants of my only visual evidence for the appearance of a large full-page miniature from the same Christie's sale as in a previous post.
It appears that Mary has her left hand to her cheek, and it looks as though John has an unusually large halo, or perhaps there is a figure standing behind him wearing a pale cloak.
Here is the Christie's description:
Even though the image is not at all clear, the presence of the date "1480" and letters "J.K." should make a definitive identification possible. If anyone has a better image, or knows where this leaf is now, please let me know.