For 65-66, the 22F battery had yellow caps and 24F had red caps.
24F was a production option, as Bob alluded, there may have been options, such as A/C that required the Heavy Duty battery option. Otherwise, unless specifically checked on the order sheet, cars would come with a 22F.
There is no reproduction of the 22F currently. The reproduction topper with yellow caps is made to fit a 24F size battery, which doesn’t make any sense.
I’m sure we’ll start seeing the yellow caps used incorrectly at shows. In judged concours classes, there will be deductions.