Looks like you found one. I had that same issue before I ended up swapping the slant for a small block. I was told you can swap the head for an earlier head and keep the hydraulic lifters and rocker arms etc. That way use an earlier valve cover, which is MUCH easier to find. If I remember correctly it had to be a pre-'72 head to fit the lifters through.
Yes, I did. Thanks for the idea on using the older cup style plug head, I think that is so that the hydraulic lifters can be changed out without removing the head and the newer head won't allow them to be pulled without removing the head
