Let me take a stab at answering this.
1) I went to our local NAPA store and the counterman sold me a PCV valve for a 351W. He said it was for just about EVERY 351W. If you need, I can pop it out, read its number, and report back.
2) I too got a breather cap that the PCV valve fits in.
3) When I got my car, I was told that it would not require a PCV valve. But, within a few months, there was a fine layer of
oil on top of both valve covers under the breathers. The PCV valve cures this and now the valve covers remain clean.
I hope this helps,
Steve