Okay, first off, you've got stovepipes on your valve covers, so any of the "twist on" or push in "grommet" types are a no go without reworking everything. So you're limited to the early-mid 60s stuff.
Second, are you looking for breathers, or PCVs, or both?
The one you have listed from
shakerhood.com will work, and is average market price for the piece, considering it has the cap and PCV valve. If, like you say, you can find the correct repro PCV valve for $20, then just get the cap and sve yourwself some cash.
[URL]https://www.megapartsusa.com/proddetail.php?prod=187-337-1064-1[/URL]
Breathers will depend on if you just want just a breather (which it looks like you already have), or a breather with a nipple- both are available.
[URL]https://www.megapartsusa.com/proddetail.php?prod=187-337-1064-C[/URL]
[URL]https://www.megapartsusa.com/proddetail.php?prod=187-337-1068-C[/URL]
There are other sources as well, here's a few on EBay:
[URL]https://www.ebay.com/itm/18562...9B9e4ezRTLTpG5fErFuCaIiiU=|tkp:Bk9SR_jP9JGUYQ[/URL]
[URL]https://www.ebay.com/itm/23350...plO2DCnx84gjCOJKrpHXnX+n4=|tkp:Bk9SR_jP9JGUYQ[/URL]