to answer #1 and 2,
1) Not sure when the vented valve cover was last used... I know is was used on my 54's original engine. But someone could have replaced your original one with a 54's cover... same bolt pattern if I remember right.
2) where did you find that number... on the head? cause that seems like a head number, the 848 head, which is the better head on these stove bolts.
3) I'll let someone else comment
