I bought the same NAPA shoes a couple of years ago and found the same problem. At the time, i checked the other retail part stores and found the same shoes. They all had part numbers that were a variation of Napa's 419 part number.
This thread from last year talks about the same shoes.
https://67-72chevytrucks.com/vboard/...ighlight=shoes
The shoes seem to work OK when driving. Having disc brakes on the front may be a factor on that.
I did find that when parked, nose up on a hill the e-brake had to be applied extra hard to keep it from rolling back. You don't always have curb to turn the wheel against.
I think it sucks that they can't give you the correct lining length for the rear shoe.