Wagner Rear Brake Shoes

That's correct. The self adjusters were changed to the new style in the 1969 model year. It's mentioned in the Master Tech series and/or in the Service bulletins (see the Hamtrack Historical website for those).

In 1968, the shoes had a minor change from earlier years by using three tabs to rub against the backing plate. For 10x1.75" rear drums, the correct FMSI frame number* is 256 up to Feb 1967, 288 for '68, and 331 from 1969 up.
I've been given 151 (Ford style) shoes and 331 shoes from most parts stores. Both will work with the '68 and earlier set up (just remove the pin on the 331 as you did), although Chrysler did disapprove of techs using 'other brand' shoes frames.

*The frame or backing plate number is an accepted standard. Often its worked into the aftermarket manufacturer's part number, but not always. You'll usually find it stamped on the metal as well.