Good summary Ian. Your right, nothing new has been forthcoming in this thread and that's the real issue.
My xu1 has a 20F3 dual cast block in it. its JP 387... This is the one that James was asking about. It is interesting that his engine number is 36.. and mine 38.. and yet they are the same date code on the block. Not to sure how to explain that, maybe the dual casts were put aside until needed, I don;t know.
I have posted pictures previously in the other disappearing thread and can do if you really want. It does not prove anything as i believe it's agreed by all that there are engines out there with dual cast dates and engines without.
/Rob