According to this site: http://www.mustangsandmore.com/ubb/DanJonesSteeringBoxRatios.html
2. Late 1967 through 1970 are the short shaft style. There is a couple
between the box and the steering shaft. This change was made to meet
Federal Motor Vehicle Safety Standards (FMVSS) which required a
collapsible steering column. Sector shafts were either 1"
or 1 1/8".
There are four different '67-'70 short worms used (2 ratios, 2 sector
I guess this means there is an early 67 box with a 1' sector shaft. I have never seen one of these offered as a rebuilt or reman box. Your just gonna have to locate one on these 67' boxes, assuming that's what they are of if they indeed exist, and find someone to rebuild it.
I am not sure the nomenclature regarding 67-70 1' sector shafts, it just doesn't make sense. 67 was a weird year because of the upcoming federal mandates for a collapsible steering column. It is my belief that compliance with these mandates is where the 1' sector shaft box comes from. When I was in the market for a 68 column, I mistakenly assumed that the 67 columns were the same. Wrong, there was a 67 only column, not collapsible, but no long shaft on the gearbox... I had to cancel a buy on eBay once myself and the seller learned this.
I've heard decent things about this guy, don't know anything personally though. If anyone would know whether your animal exists, he would.
If it does exist, and you need a core or possibly a working unit, maybe these guys can help
They have a huge inventory of Cougar parts, which, assuming you don't already know, share the suspension and steering components with equal year Mustangs.
Anyway, contact one of the previous, they would likely know one way or the other.