I'll try to find the issue where the Argentinian guy wrote in about the hydraulics. He indicated that most Y's had the solids & that the hydraulics were late blocks only. Again, who knows? Could be B.S., as I don't recall him ever sending in the pictures.

Apparently the older Y heads look like ours do (dunno if they're identical or not); as you said, the later ones (& maybe most of 'em for all I know) have the SBF similarities.
The conventional heads were supposedly later and "high performance", which term can cover a multitude of sins. Again, could be B.S. These apparently are not the Weslakes, which I have seen pics of. If I recall correctly Bill Smith of Speedway Motors has a set. I'd love to see his whole collection; talk about one-offs!

Try loading the pics in your FTE gallery & linking them or posting them directly on the page. You can copy & paste the pic number; there's instructions in the gallery if I remember right. I'd like to see 'em.

Regards, Mike