You learn a new thing everyday! Just when you thought you knew everything about Mustang II's http://cgi.ebay.ca/1974-1978-74-75-...ryZ34206QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Yeah, the vented ones are hard to find. They were only used on 76 Cobras and some very early 77s, and even then not ALL of them got the vented.
Yeah, those are an oddball. My '78 Cobra had what's left of the vented type and a regular '77 hatchback I saw in a wrecker had it too (I grabbed it and the spoiler). Seems like these were only on spoiler equipped cars and not on every one either. The vents themselves are only holes so it's easy to replicate with a standard valence and a die grinder.
time capsule I sold my 76 cobra back in 1983, but before I did I bought from Ford the black plastic valance as mine was cracked. It was just like the vented one shown. Dealer charged me $45 for the piece, and it came with no hardware. My original one was white and it was cracked, as I recall the original one on my 76 cobra was not vented. I liked the vented one better and as recall there were 2 versions one with the spolier (had predrilled holes) and one for cars without spoilers.
Wow only $45, If only we all knew how hard they are to find nowadays. I would have a bought a lot more spare parts back then. Of course back then (bought my first II in '85) I didn't expect to still have it 20+ years later!