My 428 HCS has a gray battery heat shield. Been on the car since Jan of 1970. Are you saying that they never came with one from San Jose?
Didn't say never

Stated (long version) that after 30+ years of this and digging through yards I've never seen or heard (until this moment) of a San Jose car with a gray one. Likely seen/found 200-250 67-73 battery shields over that time. Think I've got about 30 at home presently.
First one fo those I saw was at Perkins in the mid-80's.
The only place since has been in a couple of magazine articles and on a couple of original Dearborn and especially NJ 68-69 Mustangs.
Didn't all 68 Mustang V8s use the same neg cable?
Sorry we were sort of getting off (68) track with some of the hard to get items. Forgive me
Which belt was it missing?
Didn't check the numbers against the list but just looking at them. Not the best picture (better individually) but here is the group of them. At least two different makers/providers by the looks of things