Looked through all my 67 289 pictures and I could not find a single car (where that detail could be found) that didn't have the rectangle style FoMoCo on the top of the breather cap with the 90 degree bend in the neck/connection. There were dozens. One such example is shown in the thread that follows http://www.concoursmustang.com/forum/index.php?topic=8272.msg47869#msg47869 5th picture down
Does not surprise me that service replacements (NOS) were different as this follows the pattern we see on a number of other 67 parts. Of course this is an easy piece to change out. Put on something, if this is holding up things, keep progressing and change out then you find one.
Think the challenge is that this was such a common piece that few saved it or paid attention. I would guess you'll eventually just fall across one or find one from one of the parts providers on EBay that seem to sell every last piece they can detach from a parts car. Purchased a couple of pieces like this for under $20 total with shipping from one of them over the weekend.
Keep the faith - don't settle and you'll find it
Appreciate the effort in looking, Thanks Jeff.
It was my understanding that the 'rectangular block design FoMoCo' was correct, hence my hesitation in pulling the trigger on the NOS part. I suppose the search feature (again) chould have first been "my friend" before asking the question, the other image I used in this ad wasn't clear enough to tell.
My "Mustang A.D.D." tends to kick in when I begin to search for things like this and I suppose my obsessing can get the best of me at times.
I wish I knew what actually happened to the original but my thoughts are now that it must have disappeared in '97 when I last had my engine out. The car was parked the following year (1998) and I was having carburetor problems with a Holley I had been using, often running without the air cleaner at times. Recently, by using pictures taken during my tear-down, I realized I had installed another breather cap bought at a local parts store because it went missing during the engine rebuild (forgot that detail). I only figured out it was even missing just last week. (now I'm sorta pissed after my memory kicked in about loosing it ~sure glad I don't have these memory lapses anymore, I gave up the booze +17 years ago now!)