May I interject that I have wanted to replace the 20MM nipple that's the PCV mounting spot. I don't like having to use multiple clamps and adapters to get to a 3/4" or 5/8" hose. I tried to pull one of these nipples out of a case and it wouldn't budge without my destroying it in the process.
Looks like the 20mm hole would have to be drilled/reamed and tapped for a 3/4 NPT or a fitting welded to the existing steel nipple and that pressed back in. Another option would be something custom turned to fit. If you wanted a hex on the piece it would have to be 1" to start with. It would also have to be high enough to clear the rib on the case so a socket or wrench could fit on it.
If it could be screwed out then you have more options for accessing the oil galley hole next to it. I have a lathe and TIG so I am really tempted to do something...