Here is some more information on the "Competition" handling package that I found on the web; sorry, I don't remember the source.
"A 1967 Mustang GT with Thunderbird wire wheel covers?
In 1967, Ford offered a "Competition Handling Package" that was optional for GTs only - in which case it upgraded the regular Heavy Duty Suspension that was standard with the GT Equipment Group. This Competition Handling Package was expensive and seldom ordered. It consisted of extra stiff front and rear springs and adjustable shocks, an extra thick stabilizer bar, a 16:1 overall steering gear, a low speed rear axle (no lower numerically than 3.25:1) in a Limited Slip differential, and 6xl5-inch wheels with wire wheel covers.
The strangest part of this option was the set of wire wheel covers, which are unlike any ever seen on a Mustang. They were actually sourced from the Thunderbird line because Mustang wire wheel covers fit 14-inch rims.
Here is what I believe the Competition Handling Package wheel covers looked like. Notice the similarity between it and the '67 Shelby 15" wheel cover? IMHO, only difference is the center cap.
'67 Tbird wheelcover 15"
[Blocked Image: http://img297.imageshack.us/img297/8673/67tbirdhp4.jpg]
'67 Shelby wheelcover 15"
[Blocked Image: http://img297.imageshack.us/img297/9353/67swc1jpegfw7.jpg]