1971 Rear Wheel Cylinder, Rubber End Caps

I am rebuilding the rear brake wheel cylinders for my 1971 Plymouth fury.
I purchased NAPA rebuild kit 491. The rubber end caps are too big and will not attach to the end of the wheel cylinder. Store manager tried to help, but found nothing.
I'm looking for seller and part number for a kit that has correct rubber end caps.
Dorman 3608 appears on eBay. .FCBO search does not show anyone using this kit. Has anyone used this kit? Were the end caps right?
Drum Brake Wheel Cylinder Kit-Repair...

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Author: 1970FuryConv